Q: Is it possible to play 2 seperate iTunes libraries from one iPad?

the best wy is to build a library from both ids on a computer via itunes then sync your devices to that computer.  see this

http://support.apple.com/kb/HT1206?viewlocale=en_US

Peace, Clyde

iTunes purchases are tied to the AppleId used to make them and cannot be transferred. iOS only allows for the use of one AppleId for a specific purpose at a time (i.e. you can use different IDs for icloud and itunes for example, but not two on each function). Changing the AppleId on an iOS device for a specific function - in this case itunes - precludes being able to use the old one for 90 days on that device.

You can, to a degree, do what you are talking about, but only via iTunes on a computer and syncing: http://support.apple.com/kb/HT4895

Yes you can, but once you do, you will not be able to log back in with the first AppleID for 90 days. Once the tracks are actually downloaded and in the Music player, it may not matter (not sure). But in terms of downloading it will limit you.

iPads and iPhones are pretty much explicitly design as single user devices.

You would have access to music already downloaded on the iPad (I think), but would not be able to buy any new music on the prior account on the ipad for 90 days (the AppleID itself would be fine). If that makes sense.