check out tomshardware.com for info regarding video card performance and memory. They have good info regarding the latest motherboards too.
in conjuction with that, its nice to read reviews from newegg.com on the products before you buy them.
Most likely, the ram you recieved with the VAIO is cruddy (slow), so expect to replace that. Determine the motherboard you are getting before you decide on the ram.
I think your cpu speed is fine for now.
I currently have a Sony VAIO that I got a year and a half ago. Specs are:
PCI GeForce FX 5200 128mb which I added.
I'm very into Half-life 2 and CS:Source. I would like to upgrade to AGP.
Could anyone recommend a motherboard, a soundcard, and a video card? I would like the video card to be around 150-200. Also, do I need to replace my processor? I would also like to add more RAM (maybe another 512mb).
Thanks in advance