Vasanth Dharmaraj has implemented an application that runs Mozilla and IE, for the convenience of having only to run 1 application to check how your websites render in these 2 web browsers. Read the initial entry (with screenshot) and the entry on how to get it.

I haven't tried it, simply because it requires the .NET Runtime to be installed - I've run out of harddisk space on my laptop. It really sucks when your 80GB harddisk goes offline - my desktop computer just died for no reason a while back and my anime store, not to mention my CD-writer, are now inaccessible to me.