Help with Modifying 3.5

[Kendall-DM]

I have two main things in 3.5 that I wish to modify, but for the life of me I can't find where the original things are. So, I'm asking the community for some help. Here goes.

I want to modify the attack bonuses from attributes so that they are one-half what they currently are. For example, an 18 Strength normally gives a +4 to your attack, but in my homebrew it only supplies +2 (half as much). My rule is thus, all bonuses to attack values are halved, rounded down, but at least providing a +1 if you have a bonus (so that 12-13 range still gives +1). Notice this has no effect on penalties, only the bonuses. So I need to 1) code a conditional into the attack bonus calculations, and 2) adjust those bonuses appropriately. Any help for where (or if) I can do that would be appreciated.

Secondly, I have a modified skills so that base classes have class skills, cross-class skills, and general skills. The class skills and cross-class skills work normally, but my general skills are bought like class skills, but are limited to the max ranks of a cross-class skill. Any clues how I can implement that would be appreciated. I know I can define general skills in the base classes, just not sure how to implement them code wise (again, I seem to have trouble finding where exactly the system code does its thing).

I'm familiar with XML, but not fluent (I only just learned the basics this past fall). I am a programmer, so any help won't be too far over my head. Lay it on me. Thanks.