How much memory to build into my new machine?

[sunburst79]

I'm going to be putting together a new machine. At the moment it looks like a ASUS P5W DH and a Core 2 6600 (2.66 GHz).

My question is how much ram to use, I'm planning on using lots of VI's in the future so capacity is important to me. I currently have have 2 1 Gb sticks of Corsair XMS-6400C4 on hand. Should I buy another pair or a single 1GB stick?

I'm trying to avoid some of the problems I have heard of that people have had with around the
Windows 4 Gb limit.

Maximum or 2 GB OS- 2 GB Applications right? Do I want to run 4Gb or 3GB?

I'm aware that Windows normally wont show all 4 GBs

Any help would be appreciated!

Another Question? ASUS list that this board will still run in dual channel mode with only 3 slots populated. Am I missing something here? I was always under the opinion that you had to an even number of pairs installed in order to to run in dual channel mode. Do have my terminology mixed up?