Tough choice. The faster RAM is good, but with the 2 GB sticks you have the option to add more and have as much as 8 GB, at least with most good P35 motherboards. Your x64 OS can use 8 GB already.
I think I'd go with the 2 GB sticks, just because I expect software to become more and more bloated in the future. (And I'm not only thinking about Microsoft. For example my X-Fi drivers take 800 MB. I remember my first soundblaster came with drivers on a floppy disk, 1.44 MB)
Edit: deuce271 beat me to it, I hadn't seen this reply when I was typing mine.
I may have misunderstood your last post, but if you mean you are looking at going for a board that is compatible with both DDR2 and DDR3 ram, I would pass.
I originally thought it'd be a great future proof idea to buy one of these boards, but most of them will support 8GB of DDR2 memory and only 4GB of DDR3 memory. I'm thinking by the time DDR3 memory becomes affordable, you may already be looking at getting 8GB for the reasons aevm posted above. This is a big reason why I went with the GA P35-DS3R over the GA P35C-DS3R mobo. Essentially I saved $30, and got, from what I've heard, a more stable and better OCing mobo.
I have a quick question. What if the speeds are exactly the same for the 1G and 2G sticks of ram. Will using 4 sticks of 1G be any slower than using 2 2G sticks? Or nowadays with modern motherboards does this even matter?