Well, I'm not sure just where to begin...
First, you really shouldn't worry about an online rating (or any rating, for that matter). Concentrate on learning, and the rating will follow. There's really no need to use a computer as a crutch for game playing, unless you want to play games when you don't have internet access. Plus, you'll probably learn faster by playing people instead of a computer.
Second, if you really do want to get a chess program for a sparring partner, you might want to try out a free alternative like Lucas Chess. (I don't use it, but many here do use it.)
http://www-lucaschess.rhcloud.com/index.html
The problem with Chessmaster is that you can't buy it through the retail channels any more. You'd have to get it via the used market. The one nice thing about Chessmaster is that the tutorials are pretty good.
If you can't be deterred from getting Chessmaster, I'd recommend getting Chessmaster 10th Edition. It's a lot cheaper than Chessmaster 11 (also called Chessmaster Grandmaster Edition), and it runs just fine on Windows 7.
I'm have a crappy 967 rating (that's because I'm a crappy player) in 30 minute games.
A friend advised me to get a chessmaster program for my PC so that I could practice up against chessmaster's beginner computer without losing rating points.
I have windows 7. I looked up chessmaster and can't figure out which chessmaster version to get that will work well with my PC. Any suggestions?