What would you upgrade?

[Linken]

I feel my PC is getting a bit sluggish. But I don't know which part to upgrade. I have about £150 to spend + more if I sell old part.

Spec currently:
8800GTS 320mb
E6600 2.4ghz
2GB Crucial Ballistix pc-5300
350gb seagate hdd
corsair 520w power supply
gigabyte p35-ds3r

I was thinking of selling the E6600, and getting a quad or maybe upgrading the ram. What are your thoughts?

 

[Linken]

You guys are right. It's not sluggish when I'm playing single games. The problem is, I play an MMO where I have 3-4 clients running, additionally with 10 other windows/programs in the background. It does get slow.

And I'm on XP, although I have considered upgrading to Vista the last week or so.