A recent update to MSN's home page requires the latest Flash Player, older Flash Player version 6.0 versions will crash windows explorer while attempting to load the page. Go to www.adobe.com and download and install the latest flash player 9.0 to resolve this issue.
I had the same exact thing happen to me today. I tried updating to the latest Flash player. It said it successfully installed but it didn't help. Every time I leave the MSN home page and go back to it (either by hitting the back button or going via the link in favorites), the browser crashes and restarts. Pretty annoying.