I'm trying to put some background music in a game I'm making which for me involves clicking around http://www.jamendo.com until I hear something I like. I've been assuming I can still try to sell the game if I don't use any music which has a Noncommercial license. I just want to confirm that if I get music with this license: http://creativecommons.org/licenses/by-sa/3.0/ that I will be able to sell copies of the game. The part where Share Alike says "you may distribute the resulting work only under the same, similar or a compatible license." to me implies that I would have to make my game creative commons as well. Or, does this sentence just mean I can't alter and sell the song? If I want to alter the song to make it play well in a loop or something, would that effect being able to sell the game?

It depends on what CC considers derived works
If a game is considered a derived work from the music then you have to relicense the game under CC Share-Alike license
You can still sell the game but the moment the buyer gets the copy he would be able do upload it legally on any filesharing site(off course it would end up there eventually anyway)
Your best bet would be to just contact the authors so maybe you can make a deal with them

I agree with the previous poster for the most part, allowing them to import their own music banks is often an easy solution (and fill the temp with PD licensed music). But something else I have found is that most of these artists who release their works under free license types never expect income to begin with, and hence are willing to part ways with non-exclusive commercial licenses for ridiculously low prices. One of my friends (who builds flash games for a living) claims to offer these guys $20-40 & credit for a full nonexclusive license. Just something to consider.