Vista users: can I install two different versions of Windows Media Player on Vista?

I'm using Vista which came installed with WMP 11 - but when I go to mtv2.com video section it says I need to use WMP 9 to view content. My question is can I run two stand alone versions (I don't want to install 9 and lose version 11).. Why wouldn't WMP 11 allow me to view content that 9 can? Does anyone else have this problem?