http://forum.ppcgeeks.com/showthread.php?t=20550
This should be the shrine you look at for info! It's a good place to start looking if you are new to the whole developing thing.
You have two methods to put your regedits into a custom ROM.... an RGU file or a PROVXML file.
rstoyguy should have a good article about RGU creation while AceszHigh and myself should have info for the PROVXML part.
Don't forget to thank the person w/ the article that helped you out the most. I know rstoyguy and AceszHigh would appreciate it!