Woohoo! Another Lankhmar enthusiast!
I'd have to agree: the 1st ed.
Lankhmar: City of Adventure book works out great. However, I'd recommend having a copy of that and of the 2nd. ed update (with the same title, but more of a stylied font on the title; also, 1st. ed. book is grey; 2nd ed. book is black--both softbacks).
IMHO, the Lankhmar boxed set is, well, lacking. Great if you don't plan to use anything else ever with it, but not good at all with the rest of the Lankhmar material.
The big thing about Lankhmar in 1st & 2nd ed. is that it's kind of choppy--doesn't quite mesh well with the way the system worked then. Using
Skills & Powers w/ the 2nd ed. AD&D version of Lankhmar (plus the S&P stuff in
Spells & Magic) worked out well because it easily allowed PCs of some classes (like bards, rangers, etc.) to easily swap out their spellcasting abilities for other non-magical abilities; the S&P stuff in Spells & Magic allowed for a more accurate build of white wizards, black wizards, & elemental wizards.
The other Lankhmar items (supplements, modules, etc.) are decent, & may be usable if you're going to run an older-edition game, but other than the flavor text/fluff, you'll pretty much have to convert everything over to a different edition.
IMHO, the best stuff you need to run a Lankhmar campaign is the actual books themselves (or knowledge of them). It gives you a great feel for the feel of the lands of Nehwon, as well as the folk of Nehwon.
Now, if you're going to use 3.X for a Lankhmar game, there's at least 2 options that I know of for such campaigns:
Option 1: Grim Tales
Can't tell to much about this one. (Wulf... paging Wulf.) Word of mouth says it's great for that sort of grim, gritty, pulp-fantasy, classic `30's sword-&-sorcery style of stuff (of which Leiber's work fits in perfectly.) IIRC, it's d20 rather than D&D, so it's a whole new ball park. Magic is treated as a learnable skill rather than as a key aspect for a base/core class (unlike D&D). I can't say for sure, but I think combat may be much more in-depth (compared to you-attack, you-hit/you-miss basics of D&D combat).
Option 2: 3.5 D&D using optional rules from Unearthed Arcana
This is what I've been working on for quite some time. If you want to use D&D for Lankhmar, then IMHO, this is the best route to go. There are specific options I'd recommend using, & some others that may add to the game.
- Generic Classes: Best thing to use for Lankhmar in D&D. Allows the players to virtually build any sort of character concept in the Nehwon/Lankhmar genre. Warriors & experts can be used as is, while I'd recommend some limits on the Spellcaster class to replicate the white/black/elemental magic of Nehwon.
- For spellcasters in Nehwon: First off, all magic is arcane (i.e., no divine magic, & thus, casting spells in armor). Second: player must determine what kind of mage he/she is making, which determines what attirubte they use for spells, AL restrictions, & spell restrictions: White wizards use Wis, must be Good-aligned, and learns spells from the Druid list; Black Wizards use Int, must be non-Good aligned (and then switch to Evil-aligned by 5th level if they want to progress up to 6th level & beyond), & learns sorcerer/wizard spells; Elemental wizards use Cha, must declare what element/energy they will focus in (air/electricity, earth/acid, fire/fire, or water/cold), & can learn any spell from any list, but at least half of their spells (rounded up) must be of their chosen element. Also, they can never learn any spells from an opposing element (air vs. earth, fire vs. water).
- For ease of play (& ease of running/starting a game quickly), only allow human PCs (BTW, there are no dwarves/elves/orcs/ etc. in Nehwon; there are ice gnomes & Nehwon ghouls, but those are new creations that you'll need to create on your own--the original books should give you a good idea of what these races should be like).
- The Character Traits & Character Flaws are a good mechanic to use with these characters.
- Lankhmar/Nehwon is low magic, so ACs will drop behind BABs because of the lack of magic armor. To dofend against that, you may want to use the Defense Bonus rules from UA (in addition to other rules such as Armor as Damage Reduction, and alternate HP/injury systems like Vitality and Wound Points, Resrve Points, or the Injury System have potential as well). Or, a simpler way to accomdate the low-magic feel is to just have PCs roll for their Defense (i.e. add all armor, Dex, & other defensive mods to a d20 roll rather than a base of 10); you could allow PCs to just "take 10" & have a standard AC score, or "roll with it" and add all of their defensive mods to a d20 roll for their AC (for that entire round, of course). (See pg 25 of the DMG for this.)
- Action Points (ala d20 Modern & Eberron) work great for this setting. It just fits perfectly.
- The Contacts & Reputation rules from UA also work well for PCs. Since the charts are tied to the PHB core classes, here's what I'd recommend: For Reputation, use Column A for commoners & other low-rank NPCs. Use Column C for all PCs. A PC can choose to spend a feat to have a higher Reputation (using column D) or take a Flaw for a lower Reputation (column B). For Contacts, same concept, but opposite alpha-tags: column D for commoners/NPCs of low rank; column B for all PCs; column A for PCs who spend a Feat on Contacts; column C for PCs who take a Flaw on Contacts.
- The Taint rules in UA are a very good idea for Black Wizards (and any of their spells/magics). Having Black Wizards acquire Taint from their powers fits in well with Leiber's setting.
- Incantations are a great way to have non-spellcasters perform magical effects, as well as a way to incorporate powerful spells into the setting: the cultists that summon the Cloud of Hate is a good example; the Snow Witch circle & their potent cold-weather magics is another.
- And, regarding Alignment: you may want to use the Allegiance rules from d20 Modern instead of Alignment; it works great for more shades-of-grey settings like Lankhmar, and allows for PCs that hold true to their loyalties & not necessary violate those beliefs (unlike Alignment, where the PC may do something loyal to a group/friend, but not to his/her AL). However, White Wizards must have an Allegiance to Good, and Black Wizards cannot have an Allegiance to Good (and must have an Allegiance to Evil by 5th level if they want to progress to 6th level & beyond).
As for the setting itself, I personally prefer to run my stuff
after Fafhrd & Grey Mouser have retired to Rime Isle--it allows the PCs the chance to become the big-name heroes of the time (and, it allows me to have Ningauble & Sheelba's weork as the PC's new patrons/employers/quest-assigners). Less NPCs to concern yourself with as well (a fair number had died off by the end of the series, so that's less to concern yourself with converting, & allows you a bit more wiggle-room for creating new stuff overall). But, it's complately up to you when you want to have your campaign set in Nehwon, whether it's during the Twain's ealrly years, at the height of their abilities, or during their retirement (or even sometime far before/after then).
Hope any of this is helpful for ya.