You can have two iTunes libraries on one computer if you also have two user accounts on that computer. iTunes will create a separate library for each. That's a new Windows user on the computer. Not a new iTunes ID.
The initial setup will be a pain, as the empty library you get when you sign in as a new user on the computer will decide the iPad needs to be erased. You get around this by forcing a Transfer Purchases. Also, you need to authorize the computer in iTunes, again, and it will count against your total of 5 computers allowed to access that iTunes account.
Marilyn's solution is easier. You just have different sync profiles. iTunes remembers what you set to sync on each device, mostly. There are occasional hiccups with new purchases, but they aren't that hard to clean up.
But if you want a separate iTunes library on the same computer, that' how you do it.