Fairly straight forward calculation.
Class skill amount + int bonus skill points (+3 at first character level).
Int bonus for 20-21 int is going to be +5 at levels 1-7, +6 for 22-23 int from levels 8-15, +7 for 24-25 int at levels 16-20.
Headband of intellect providing enhancement bonus to int in 3.5 does not affect skill points.
Headband of Intellect
This device is a light cord with a small gem set so that it rests upon the forehead of the wearer. The headband adds to the wearer’s Intelligence score in the form of an enhancement bonus of +2, +4, or +6. This enhancement bonus does not earn the wearer extra skill points when a new level is attained; use the unenhanced Intelligence bonus to determine skill points.
Moderate transmutation; CL 8th; Craft Wondrous Item, fox’s cunning; Price 4,000 gp (+2), 16,000 gp (+4), 36,000 gp (+6).
The wild card would be inherent bonuses to int from a Tome of Clear Thought or wishes.
Tome of Clear Thought
This heavy book contains instruction on improving memory and logic, but entwined within the words is a powerful magical effect. If anyone reads this book, which takes a total of 48 hours over a minimum of six days, she gains an inherent bonus of from +1 to +5 (depending on the type of tome) to her Intelligence score. Once the book is read, the magic disappears from the pages and it becomes a normal book. Because the tome of clear thought provides an inherent bonus, the reader will earn extra skill points when she attains a new level.
Strong evocation (if miracle is used); CL 17th; Craft Wondrous Item, miracle or wish; Price 27,500 gp (+1), 55,000 gp (+2), 82,500 gp (+3), 110,000 gp (+4), 137,500 gp (+5); Cost 1,250 gp + 5,100 XP (+1), 2,500 gp + 10,200 XP (+2), 3,750 gp + 15,300 XP (+3), 5,000 gp + 20,400 XP (+4), 6,250 gp + 25,500 XP (+5); Weight 5 lb.