Based on a college-project I'm trying to realize a relatively simple game (Poker) where an iPad acts as Server and multiple iPod-Touchs connect to it as Clients.
Gamekit seems to drop out, since those old ipod-touch-devices don't have bluetooth-support.
Are there already some Frameworks out there simplifying the process, or do I have to fall back on TCP-Streaming-Sockets and implement it myself?
Distributed objects are not yet available on iPhone OS, so excluding GameKit you may try using Bonjour networking. Otherwise, you may try using web services with some of the available libraries. If Bonjour and web services are not a choice/possibility, then you have to revert to old plain sockets.
For your task I suggest you have a look at ThoMoNetworking or AsyncSocket.
ThoMoNet is a very simple setup that is specifically developed for fast and easy prototyping and easy to set up. Is will automatically create a bi-partite graph between all instances of you application it finds in the local network. So If you keep your iPad as the server and the iPhones as clients this will come down to less than 10 lines of code to set up.
AsyncSocket is a commonly used framework with ports to PC as well but requires more code to write. On the other hand it will allow you to do more fancy things, should you need them.