Google Music support was just announced for the Android Market. You can preview and buy music right on your phone! Right now you are probably asking "How can I get it?!"
Well, normally we would have an APK download for you, but this update is totally server side. Anyone running Market 3.3.11 is ready to use the Music Market. Google is it out to accounts right now. If it doesn't work for you, just have to wait. Sorry.
Mine did update though, So I might as well show you some screenshots.
It looks exactly like the market does now, the music section is just orange. You can buy tracks and listen to 90 second previews, depending on the song. If you click "buy" everything works exactly as it does in the normal market, except the music gets synced to your Google Music account instead of the Market.
See? Exactly like the Market, just Orange.
Actual album pages look a little different than your standard Market page. In the grey section is the buy album button. At the top of the list there are the individual songs, which you can tap on for previews. In line with the songs are individual buy buttons, if you only want a certain track. Below that is the normal Market stuff, ratings, comments, etc. Some pages are special and have a video and a description at the top of all this.
So that's the new Music Market. Like we said earlier, there's nothing you can do to make it update. Just wait and the music will come.