DDR3?Gah!? I don't wanna replace my motherboard...would I HAVE, HAVE to? I don't wanna dismantle my PC all over again......
......Luckily I've already replaced my RAM a while ago, to 8GB.
And yeah, to get any appreciable upgrade, you will *have* to replace your motherboard.
AMD's current line of procs is more or less on par with the Phenom X4s. They are also really picky about which motherboard and chipset you have. If your mobo isn't 990FX, you run the risk of it basically catching on fire with some of the FX chips.