I am using Windows all my life and switching to OS X (Leopard)

So I will do my best to use it totally but my very main concern or my biggest need from windows will only be the need to test the websites on IE6, IE7, Firefox on Windows (Cross Browser Compatibility)

So I need advice on which is the best method to do that?
1- Using Parallels?
2- Is there Emulators?

or what to do?

I read that Parallels will do the work nicely, but I don't like the idea of buying it and installing another operating system (Win XP) just for sake of testing, so i was hoping for other alternatives within OS X if possible?

Thanks in advance