I can't get your links to work. You need to use hxxp:// instead of ht*p, because the links get broken. Luckily NewEgg's search function was still helpful.

Until an OS that takes full advantage of 64-bit processors comes out, stay away from Sempron64. It's like buying a new processor when it first hits the market.

hxxp://www.newegg.com/Product/Product.asp?Item=N82E16819104252
>This one is $63 and is a Sempron 2600+, 1.6Ghz. Does not support SSE3.

hxxp://www.newegg.com/Product/Product.asp?Item=N82E16819104249
> Same $63, same as above but with SSE3 support.

With a 939 socket, you could step into this for $146:
hxxp://www.newegg.com/Product/Product.asp?Item=N82E16819103537

All of AMD's development is going to Athlon64. If you doubt that, I suggest you visit Tom's Hardware and read up on the Socket M2. Looks like some of the newer boards will give the Xbox360 a run for its money.

btw, I would kill to get one of these.