Ok, first thing, it looks like you started two topics about that. I don't know if that was intentional or not, but you should probably try deleting the other one.
Now, to get this straight:
You have a 1ghz machine that was running winxp on a 10gig harddrive. You then took out the 10gig, put a 40gig in it's place, then tried a fresh install of winxp on the 40 gig. You got no errors, but now when you boot it won't boot?