A couple of additional points...
The 14" iBook does have a bigger screen but it has the same maximum resolution as both the 12" iBook and PowerBook. Also, you'll be able to find a comparison of the the Radeon Mobility and GeForce Go somewhere but one thing I noticed is that although they're both 32mb, the GeForce has DDR RAM. The PowerBook 12 is AirPort Extreme ready as opposed the the AirPort on the iBook (802.11b instead of 802.11a, I think anyway) although if you're uni only has standard 802.11 (is it a?) then that won't matter too much. The main upgrades on the PowerBook 15 is higher resolution and a level 3 cache, which is especially useful for games. Although as dlloyd said, this should be getting upgraded soon (probably June at WWDC I imagine).
Whatever you get, you'll find OSX is lovely for programming. The development environment is great and includes support for Java, C++, C, Objective C and AppleScript. There's also Ada available for it.
http://developer.apple.com/tools/