about how big is an average psp game file or psp .iso file?

From what I've seen, 600-800MB is average. There are exeptions, of course.

vary from under 100 meg all way up to nearly 2 gig (but some bigger games are ripped, ie movies music took out etc to make them smaller)

mmm some scrubs need to check themselves......***cough***ultraprime and mickymuff***cough*** c'mon, the average iso is 80mb to 1.8gb (drrr thats the max a umd can hold....)now, if you want them smaller they have things like ripkits and tutorials that will take unwanted things out, Mostly dummy files that can range anywher from 100mb to 1gb, but some take out music (which i dont like). look around its up to you what you take out, i have a 2gb stick so i just leave everything but dummy files...

I did say average that I've seen

As I have a 1.52, not really been looking