One of our engineers does architecture on the side and he went from XP to 7. He would not even mess with Vista though his wife did and she hated it. He says 7 is the best OS he's seen come out of Microsoft since XP and he loves it to death. My daughter uses 7 at her job at Purdue University. They also made the jump from XP to 7 without investing in Vista. She also loves it.
I thought about putting it on my computer but I'm still running a P4 3.4 GHz with only 2GB of memory, not enough to run 7 effectively.
Try Win7; it’ll run fine on your computer. You might not get all the cool Aero effects if your graphics aren’t up to speed, but it’ll run fine otherwise, you have enough horsepower there.
Depends on what you want to do with it. If you're only running a few applications at a time, 2GB is plenty. I run Win7 on a 2.0GHz Core2 Duo with 2GB of RAM and it does a decent job.
A 3.4GHz P4 oughta do a decent job also, as long as it's got plenty of cache. Won't be a speed demon, but IMO it's worth trying.