For testing websites, Can I test for Windows 7 on Windows 7 Starter and can it get IE9?

Yes, IE9 installs on all versions of Windows 7, so you’d be fine there.

There may be a better way to do this than buying a dedicated computer though. Have you looked into virtualization or setting up one of your existing machines to dual boot with windows 7 as an option?

Something like VirtualBox might be a simpler (and less expensive) solution.

I’ve considered things like virtualbox but my boss is not keen on it. Right now I’m looking into other options, like cheap laptops. I’ll be making a case for things like virtualbox but I need some alternatives to present him as well.

If you just need to check CSS something like BrowserShots might do the trick.

Nah, I need to check everything about the website. CSS and functionality.

Alternatives

Review Of Cross-Browser Testing Tools

Perhaps you have some extremely operating system-specific features on your website (which I hope not, as that without a doubt will be a mess), but if not, testing in IE 9 should turn up the same results even in different versions of Windows.

Right, Well the reason I ask is because there is no IE9 for XP right? I’d need 7 or vista for IE9 and I need to test in 9.

That might be the case (not that you’d want to buy a PC with XP anyway), but if you need Vista or 7, you don’t need a machine that can do both (which was how I interpreted your question).