I have Vista and am having a similar problem. It is certain tracks, and only copies a small portion of my library. It will also say towards the end of sync that the ipod can't be found. I've restored it twice. When I try to run a diagnostic on the ipod, it hangs at just under 50%. It's a 7th? Gen, 160gig ipod. This has been very frustrating. All was fine until about a week ago. Never had issues syncing.
I found my problem. It was only stopping on my latest album downloads from Amazon - once I deleted them from my music library, the sync worked without problems. I re-added the songs one at a time by opening them to play and add to the library that way. Haven't had a problem since. Both iPods are now syncing without any issues.
So I have a new iPod I didn't need; a new hard-drive that had a bad spot, but wasn't cause the issue; plus my hours of deleting/syncing/copying/etc.
If you've downloaded any songs from places other than iTunes, you might try eliminating those before buying all new stuff.