Usually the manufacturer's website will have a cpu support list for the specific model motherboard. Sometimes you'll also have to update the bios of the motherboard to get a certain cpu to work.
You definitely won't be able to put it in an AM2 socket, but I believe you can put it into an AM2+ socket if you update the bios.
Yea, I could not find that chip on the website and was hoping it was just missing!. No such luck.
Some AM2 boards will take an AM3 cpu with a bios update. Also some boards will take processors that are not listed on their cpu support list, of course you would be gambling to test this out but it has worked for me on a laptop. Here is a link to an example of an AM2 board that can be used with an AM3 cpu with a bios update.
http://www.gigabyte.com/products/product-page.aspx?pid=2755#ov
Here is the link to its cpu support list, you'll notice the bios versions needed for each cpu listed on the right side.
http://www.gigabyte.com/support-downloads/cpu-support-popup.aspx?pid=2755
Thank to all for your help. This is an MSI board with an Athlon 64X2 Processor. No L3 cache. The socket is an AM2. I got the board, Chip, and RAM for 50 bucks so I figured no harm no foul. She even gave me an HD 6770 for $70. I think I am just going to put it in a simple case and set it up for the Missus. She surfs the net and plays very simple net games so it will work perfectly for her purposes. I shall lay in wait for the next best thing to come along and see if I can build something better.
Sounds like a good idea, especially with black friday and cyber monday around the corner. Newegg had some pretty good sales last year.