Not sure I understand here. You can only sync an iPad with one computer at a time. Syncing with a second computer will erase the content that was obtained from the first computer.
You music and purchases though can be kept on up to 5 computer simultaneously. When you no longer want to use one of those computers you can:
1. Select Deauthorize this .computer in iTunes on the computer you no long want to use.
2. Go to your iTunes account and select a computer to deauthorize.
Deauthorizing a computer means you can authorize a new computer to store your music etc.