I would look for a used cpu. Newegg doesn't carry any cpus that will work with your older board. IF you find a used q6600 for around $110 with heatsink, then that's what I would try with your board. If it doesn't work, you can easily get your money back on craigslist. Check anandtech's for sale forum or your local craigslist. I would also get another power supply anyway as soon as possible. I use an ocz 400w, and found it new on craigslist for only $35.
I'm not sure you can really do anything with the way you have it set up. I'm actually surprised your system is working as it is, the 5570 needs a 400w supply. Mind you, if you're never stressing it, you can get by.
I'd really REALLY recommend upgrading the PSU to a good name-brand in the 400w range before you consider upgrading the CPU.
Anyways, with that system, there are quite a few different versions hanging around. Can you download CPU-Z, run it, and check the motherboard info? The CPU support will vary by motherboard.