No, you should not have to reinstall the OS. The Safari cache and cookies will not affect this issue. You could try running
Onxy to run the nightly cleanup items that occur when you leave you Mac on.
There are two conflicting reports regarding you machine.
Specs say no, while
someone says yes. Why importing should be an issue is beyond me, since I know for a fact that older versions of iMovie were able to import with a much less powerful machine. Bloody Apple!
Your best solution may be to import via the Macbook, then copy the files over. A hassle and you need to learn where to copy them from and to, and an acceptable workflow. The imports end up in your "Movies/iMovie Events" folder under whatever event name you choose. I think in your case they will be .dv files, but might just be .mov files. I haven't imported DV to iMovie 08 or 09. Anyway, once you have imported (via copy) from the MB, you can remove the files from the MB.