1. Ya, but it never really worked for me for some reason. Even on a LAN, downloading maps like that was kind of buggy and I could never get it to work.
2. Wouldnt know, but it works very nicely on my 15" PowerBook 1.5 ghz.
3. Yep, and if you need any more graphics capabilities just switch out the graphics card (I would go for that ATI X800 (not released yet but looks damn awesome))