What do you do with your PC if you game then a new GPU would be good if not then a CPU and motherboard upgrade would be good for you. What kind of motherboard do you have it might support some of the newer CPU's which would save you some money on buying a new motherboard.
Edit: After researching your mobo it does not support any thing over the Athlon 64 x2 6000+
How about this
Get this Combo deal
http://www.newegg.com/Product/ComboDealDetails.aspx?ItemList=Combo.240745
You can either use the rest towards a better CPU or motherboard. Another hard drive maybe another PSU depending on what brand you have.
Or you could go with this
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102824 and
http://www.newegg.com/Product/Product.aspx?Item=N82E16817341016.
Depending on what you use your computer for either one will be a noticeable upgrade.