, you cant just "move" registry hives to and fro, they aint gonna work, trust me, what you can do, possibly is to image the old installation, then WITHOUT ever loading XP, boot to the CD and do a repair install, it may be able to avoid corruption if isn't trying to figure out what the hell is going on.
Probably the easier way to get all that done (though you would have to lose all of the files u needed unless you backed them up BEFORE putting the new hardware in) would have been a full format and re-install of XP. When you install XP, it practically designates itself to that Motherboard and processor specifically. I had the same problem too. formatted, re-installed, and it booted fine. When you did the repair and got kicked out, that was probably because something about the previous install was basically telling Windows Installer "....no"