The first rule of thumb before daring to try something new is to back up you hdd, Ive been where you are right now and its not nice, i read about the problems of downgrading from vista to xp before I upgraded so took the necessary precautions, partitioned my hdd and stored a ghost image of xp on that. so when like you, I had problems mainly with software I just restored my xp back from my xp image on the partition. in less than 10 Min's.
Since then i have set this up on friends computers as they where so impressed by its efficiency