Take a look at those benchmarks. As you can see Core Duo owns in performance. I'm not 100% sure if EQ2 takes advantage of Core Duo or not, but I would be more concerned with the video card in the laptop than I would with the processor.
Processors these days have a somewhat minimal impact on game performance. I'm not saying it's not there, but video cards keep taking away more and more things from the CPU's.
So if I were you, I'd get a Core Duo. It'll likely do just as good in a game as a non dual core CPU. Additionally, you'll see a definite improvement in other things (like WinXP) with a dual core cpu.
Single core CPU's are going the way of the dodo bird.
I own a 2.5 yrs old laptop with one of the oldest gen Pentium M @ 1.5GHz.
I also got a mobile Radeon 9600pro (128 mb).
It can still handle a lot of games. Of course, were not talking super high res.
But even a CPU demanding game like HL2 plays ok (with some settings taken down) in 1024.
The GPU is however outdated by now so playing new FPS is out of the question. But with a good mobile gpu you should be fine.
Another thing; duos (aswell as the pentium Ms) are more close to Athlons in performance clock for clock. So a 200mhz increase for a duo probably corresponds closer to a 400 on a P4.
Id go for a high clocked core and a good GPU and youll be fine!