If you find that you don’t like IE7 and want IE6 back, there’s a Microsoft support page with detailed instructions on how to uninstall IE7, this will leave you with IE6:
Microsoft IE Supports Here
To uninstall Internet Explorer 7 to return to Internet Explorer 6 on Windows XP
1. Click “Start,” and then click “Control Panel.”
2. Click “Add or Remove Programs.”
3. Check “Show Updates” at the top of the dialog box.
4. Scroll down the list and highlight the version of Internet Explorer 7 that you are running, and then click “Change/Remove.” (If you are running Internet Explorer 7 Beta 2 Preview — March 20 or later, it is not necessary to check “Show Updates.”)
5. Restart your computer and IE6 will come back.