Yes, it uses Tri-Channel memory. 3x2GB is what you want. 3GB total is slightly too little for a 64bit solution (which you should have).
You should be getting "Windows 7 64bit OEM" (OEM costs less but is tied to that machine once Activated. Don't get FULL version or the "free" version. OEM. 64bit.)
I also recommend a good Heatsink and 120mm fan combo. The fan plugs into the motherboard. Read NCIX or other places to give you good reviews on these. They cost a bit but are well worth it not just to overclock.
Vapor-X versions of graphics cards are well worth it.