Ok now this one is strange, tricky and unique (I believe)!
I recently bought a new laptop with Windows 7. Last night I copied and pasted all of my music archive from my work laptop, putting them 1st on an external hard drive (USB) and then copying them across.
As I listened to my wonderful-great-taste collection I realised that some tracks played only for the 1st 3 seconds and then were currupt. Weirder still this happened on ONE track on 50% of my saved CDs.
I checked the specific tracks on the external hard drive and they had the very same problem when played on my new laptop via the external drive. I then tried to replace those tracks by downloading replacements... they still did the same thing!
To then top it all off, I took the external drive and checked those files on my work laptop this morning... they all friggin worked! Wots going on???
I seem to remember that just after the Windows 7 beta released, an update was rolled out to fix an MP3 corruption issue. It sounds to me like you may have encountered this problem, but I wouldn't expect to see it in the final release of Win7. is your system fully patched and up to date?