I've been building for ten years now. I've always enjoyed best bang for buck rather than spending a load and getting the best. I'm looking to step up some from my current spec, but not spend anything more than £200 (~$300) but if I can spend less, then all the better.
I don't know if I should just stump up a bit of money and get a 2nd hand Core 2 Quad and keep everything else, or go for a new CPU, mobo and RAM. Note that I don't want to buy any new HDD's at the moment as I don't really need extra space and the prices being so high.
If I did go the route of new mobo etc, I would like the option to upgrade to and get the most benefit from an SSD at a later date.
I use the PC for some on and off gaming, music, downloading and web browsing. Peak performance isn't a big issue, but I'd like to step up a couple of notches and be able to play future games.
I would wait before getting a new mobo and cpu. Ivy bridge will be out later this year (april I think it is). Ram is usually pretty cheap, and 399mhz is some rather slow ram. I see that your mobo supports 800mhz so maybe consider that? In the meantime you could also consider overclocking?
I have tried overclocking my current rig, but despite having a good CPU cooler, it keeps doing funny things when I shutdown (like rebooting instead) and it kept resetting back to the standard BIOS settings. So I put it back to stock.