You could use a CPU upgrade. Gigabyte says that motherboard will support a Core 2 Duo or Quad, which would be tons better than what you've got now. Also, it can support up to 4 gb of RAM, so if you could find a couple of 2 gb sticks that are compatible that would help as well. What are you planning to use it for? If you want to play games or do anything graphically intensive, you'll need a better video card too.
Your board can run 4 gb of ram; 2 gb per slot. If you can't match your old ram, find a 2x2 gb kit of pc5300 or pc6400 non-ecc ddr2 and sell your old ram to help pay for it. I can sometimes find this ram used on craigslist for $40. Your board won't work with server ram (ecc regular or registered) so don't try it. I linked the cpu support list. After checking the bios file list more carefully, your board won't work with a quad core cpu (N/A). The fastest cpu you can use is the e6700 dual core at 800 fsb. This means your cpu fsb will have to be set manually at around 250 to run at the stock speed. Your board chipset is limited to 800 fsb as the default setting. Your board can run 1066 ram, but it will only run at 800 speed unless you overclock the cpu.