Well i blew the motherboard in my PC (it was a cheapo) I've been on the search for a new one, and found the one i want. I figured while i was at it since i got my tax refund, i might upgrade my processor as well.
The Mobo i was looking at is the GIGABYTE GA-M57SLI-S4
And I'm looking at upgrading to a AMD Athlon 64 X2 6000+ Windsor 3.0GHz Dual Core
I'd be upgrading from an AMD Athlon 64 3700+ San Diego 2.2GHz Single Core.
Will i notice much of a difference upgrading to the Dual-Core? Is it worth spending the 155 bucks.

I can't say if you will see a big difference, but I have the exact same board and I just purchased another one for the wifes. Mine is running a X2 5000+ Black Edition clocked to 3.0ghz, the wifes is running a X2 3800+ which runs just fine also. As a power user the only thing I do not like about the board is the fact that you can't adjust the memory timings. You can adjust almost everything else but that. Hope this helps.

If you know how to change the multiplier on the CPU in the BIOS I would suggest the 5000+ Black Edition. It is cheaper and should be just as fast as the 6000+. Make sure you get an aftermarket cooler if you overclock it though. I have the Coolermaster Eclipse and it keeps my temps at around 40-45C under load.

IMO, the stock AMD cooler is adequte enough for light overclocking. Anywho, I've heard a lot of great things about Gigabytes mobos. Lately, they've been targeting the OCer croud, and they have th products to back it up.

Depending on what you use it for, you should see somewhat of a difference. If you game, you probably will. My question is, what kind of memory do you have and what kind of PSU do you have? You do realize that the motherboard your looking at requires DDR2, right?

Yup if i'll be getting that mobo/processor combo i'll have to upgrade my memory also. I'd planed on going with 4GB of G.SKILL
As for my PSU i have a Rosewill RP550

Dual/quad core is overrated I have a dual core downstairs and a quadcore in here and both are not much quicker than the single core machines they replaced.

I would have to agree. The only difference I saw between mine and the wifes old one (AMD Opteron 144 clocked to 2.5ghz) was that she had a lot of trouble loading certain sites that she goes to on hers compared to mine. By the way I used a Zerotherm BTF90 CPU cooler on my wifes that I just upgraded. The processor is at stock speed and at idle the temps are at 28-29C!! Never goes over 40C with a load.