How to run IE6 and IE7 on the same machine

I've been using IE7 since early betas and tended to have my main machine with IE6 and either a test machine (or virtual machine) with IE7 ..... simply because getting IE6 and IE7 working side by side is a pain ... if at all possible !!!!!
So, now IE7 is here I have put "that" on my main machine but still find sites which dont work correctly, and the prospect of cutting another VPC with XP, SP2 and IE6 was annoying .... guess what though, Microsoft have just done it for me HERE
Ok, its time bombed till April 1st 07, but its free - no extra license needed and all the work has been done. Should do nicely and give sites the chance to roll up to IE7 ready.