I had this problem last week and finally had to call Apple support (for a fee) after trying everything I could find on the Internet to no avail. If the sync had 4 steps or 6 steps (depending on the context in which one started the sync), it would not get to the 4th or 6th (i.e., beyond the 3rd or 5th) step to finish the sync. My problem was iTunes would not move rented or purchased movies to my 1st gen iPad (note: it would still sync my iPhone but I figured there was something different in the settings for that device).
Turns out, I had about 17GB of music that had no trouble syncing for the last 2 years using the same Windows 7 64-bit PC/iTunes and 1st gen iPad, but one day it decided to not finish syncing anymore. FYI, both PC/iTunes and 1st gen iPad had the latest software since before the problem occurred.
Support had me:
1) in PC/iTunes, right-click the device and select "reset warnings"
2) in PC/iTunes, device tabs, "music" tab, uncheck "sync music" (entire music library). Select "Apply."
(Note: I was on the phone with many support folks a couple of times over the course of a couple of days for about 3 hours and we tried lots of different things but this seems to be what finally worked.)
Apparently, the sync follows the iTunes device tabs (e.g., summary, info, apps, tones, music, movies, etc.) in order when determining tracks to sync (steps 3 or 5), and if it fails for any reason, the sync won't finish whatever comes after it. In my case, it was failing at "music" so the movies could not be moved from iTunes to my iPad.
So right now I have 0GB music on my iPad. Yep, that's the fix (i.e., don't use it for one of the main reasons you want the iPad, namely to have your entire music library available/portable)! I might try moving some of the music back at some point, but I'm just glad the iPad is syncing again.
