you can't just "port" a deb file over. The application needs to be recompiled from source for the ARM processor, and in many cases might need some updates done to the user interface of the application. It's a bit more involved that you think...although I can't speak from experience. I'm just beginning to learn C++ myself currently.

Some apps will be easier to move, like command line utilities or ones that don't really use the UI (OpenArena/Quake for instance...they launch full-screen and don't use window manager elements). Others like GIMP would need a heavy re-write to make them work well in 800x480.