With what You said You'll be using it for, I would:
- Replace the harddrive with a 7200 rpm SATA-300 from, 160GB or 250GB - maybe 2-3 similar spec'd for RAID
- Skip one of the graphic cards, won't benefit You much in rendering etc., only "unnecessarily" much in gaming... (You need too be a "hardcore gamer" to justify 2 of those in SLI)
- Ask Your friend if he's given any thought to a sound card... or maybe You already have a good one for production? (Low latency, (semi-)professional card.)
- Pick whatever OS that has the most stable 64bit variant - if that's Vista or XP 64bit today, I'm not sure... I'd pick a linux and find native replacement apps, would give the absolute best performance.