I'm currently working the final project for my programming class. We're writing it in Python 3.1, and I'm doing the GUI. My team's leader wants to do the whole project in 3.1, but most pyGame addons (like pyConsole) are giving me compatibility issues. 
So, my question is, can I write my frontend in 2.5 and then hook it up to the engine that's written in 3.1? Thanks for your help!
To be honest, that's probably more trouble than it's worth.
Your best bet is to get together and make a list of the addons you guys want to use and whether or not they're compatible with 3.1.  Then decide if you can live without the incompatible ones.  If you can't, do the project in 2.5, otherwise go with 3.1 and have a "Plan B" for the addons you can't use.
If you're careful you can make switching from 2 to 3 relatively painless later on when those addons add support for 3.x.
If it's a project you plan on working on for a long time (i.e. more than just a class project), I'd probably say go with 3 and try porting some of the addons yourself.  But for a class' final project it's probably not worth it.
Using Python 3.1 and 2.5 together