Awh man haha.
Your Athalon 640 is actually a better, more powerful CPU, but with those features locked up.
Sometimes it works, sometimes it doesn't, but there is always a chance your quad core unlocks into a penta or a hex core and gets some more cache. all you need to know about that is - it will be faster haha.
Your CPU will work in any AM3 or AM3+ board - that is the type of socket. You'll want to make sure it advertises being able to do a core unlock as a feature. Pretty sure most 970 and 990FX board are going to be able to do that.