Lower end moddable games for editing experience?

I was wondering if there were any good games which are slightly lower end that are moddable. I have a Dell laptop that's about 2 or 3 years old, and it can't really run higher end games. The specs are:

2 gigs RAM
1.7ghz duo CPU
ATI Mobility Radeon x1400

I'm not really interested in FPS games as much, but if you know of any (such as unreal, etc) I'd appreciate it if you could list them as well. I'm more so interested in RPG's, Action/Adventure, etc.

I'm a complete newbie to the mod scene, and modeling in general (I Start my first 3DSmax class next quarter at Art Institute of Pittsburgh) so if you could be specific on what I need that would help a lot.

I have tried looking up Source and Unreal, as someone on these forums has suggested before, however I wasn't quite sure what I was supposed to be looking for and what exactly I needed in order to start working on the mods. I'm not asking to be spoon fed the information, however I am asking for some direction in what I should be looking for.

Also, I own a PS3, and would be very interested in modding any games available for that, if there are any.