1. Your link doesn't work
2. Might I suggest MSI board or ABit if you want good OC'ing ability. People will argue with me about this so please dont post back with ASUS ROCKS! Cause my personal experience with them has been bad...and their tech support is HORRIBLE unless you speak taiwanese.
3. Your friend is insane and you should not listen to him
4. Yes you need both ram chips to be dual channel to work in dual channel.
5. Your friend is not THAT insane in that he was correct that you cannot have dual channel AND add a 3rd ram chip..they all have to communicate together so they all have to be in single channel mode...which the mobo would automatically dictate.
6. I know nothing of that website you referred to, but if you look at the bottom it says SQUARE TRADE CERTIFIED...they are with ebay and it says they have a 99.2 percent positive rating. So it looks good to me.
Now..on my last note
On a last note, is a Raedon 9800 PRO with 256MB for $300
Nope...its $266.99 at zipzoomfly.com
I've purchased from them 2 or 3 times now. Good place