Well, it's "only" a 600 MHz CPU, so I don't think it's that unreasonable that it won't unpack smoothly..
Was it a "multiple file" .rar archive your were unpacking ?

I'm running sabnzbd at home, but since I don't have a FTP client, it isn't of much use on my N900.
Having sabnzb for downloading that odd freeware Linux mp3 would be cool!