Dell Dimesion C521 Processor upgrading.

Here are my specs for my Dell Dimension C521.

I want to upgrade my single core processorto the dual core processor, but the problem is that the AMD Athlon 64 x2 processors are hard to find because they are no longer made.

I've asked this question in many other forums but all I get is confusion hehe. At one place they tell me a processor will work at the other it won't, or it's the wrong voltage or it's the wrong wattage. So a lot of confusion lol.

Here is one of the processors

http://jbrlsr.com/?aid=5336121828&bid=3342876&cid=0&tr=0&url=http%3A%2F%2Fwww.newegg.com%2FProduct%2FProduct.aspx%3FItem%3DN82E16819103210

and

http://www.cesell.com/product.php?productid=161550

and

http://www.digiconcepts.com/amd_cpus_235.htm

and

http://www.acmemicro.com/estore/merchant.ihtml?pid=3748&lastcatid=357&step=4

If you have any better processors to suggest that will actually work and are pretty cheap, then I'll be extremely happy and thankful.