I want to do a simple mod to increase the mana multiple of intelligence from 2x to 2.5. It would be nice if someone could point me out to the proper file, and any programs I would need to do so. Thanks.

What you want to do is change the http://cs.elderscrolls.com/constwiki/index.php/FPCBaseMagickaMult setting from 1.00 to 1.25.
You can do this through launching the Construction Set; loading Oblivion.ESM as normal; ppening the setting window (Gameplay > Settings...); finding the FPCBaseMagickaMult setting, then changing it to 1.25 from 1.00; then saving the Mod and selecting it to be played in the Launcher Screen.
If you're having trouble making the mod, then feel free to get someone to do it for you. It shouldn't be complicated though!

Good luck!

You can do it through the console by typing
setnumericgamesetting fpcbasemagickamult 1.25

Though if you do it this way, you'd have to input this command for each character you play.