You can, yes, but it's a bit tricky. You don't necessarily install the package itself on the GP2X, but rather you have to extract the package on the PC first, then put it on the GP2X. Depending on the program and if you're lucky you can just toss everything for the program (as well as any extra libs it may need) into a folder on the GP2X and run it there using the file launcher, at least, that's what I used for Qazoo (since I never was able to get Gaim to run)
.ipks are either .tar or .tar.gz, so you can open them with programs like WinRAR after a bit of renaming, however be sure to make a copy of the package. The only thing you can't get out of the package is the metadata, so some things may not be able to run.
When I get Qtopia running again, I'll try to explain better Good luck!