I tried some of the hacks to run IE 7 and 8 parallel but found out myself in ruined version of default IE :(. Only solution that can work perfectly is using
VMWare or
virtual pc to host different os with different web browser is quite frustrating if you need to do development then you need to setup IIS for accessing your website on the virtual machines.
But i found something thats so much awesome i cant think any hack is easier than
Xenocode Browser Sandbox.
Its a great exaple of
Application virtualzation
Not only you run IE 7 and 8 but they also give you the ability to run IE 6 firefox 2 & 3 opera crome and safari too.
Just click the start button and give it sometime to load the application and then here you go IE 6, 7 and 8 all together running.