Did you install IE 7 by following these directions /exactly/:
http://www.ie-vista.com/known_issues.html#pre-install

and by downloading the IE 7 installer from Microsoft:
http://www.microsoft.com/windows/downloads/ie/getitnow.mspx

and installing directly from your hard disk, rather than installing
through Microsoft Update?

If not, you may have a damaged installation of Internet Explorer 7. In
this event you'll want to uninstall IE 7 (which returns you to IE 6) by
following these directions /exactly/
http://www.ie-vista.com/kbase2.html

and then re-install IE 7 as above.

Do you have the same experience when you run IE 7 without add-ons?

[In XP: Start > All Programs > Accessories > System Tools > Internet
Explorer (No Add-ons)

or:

right-click the Internet Explorer icon on your desktop and select Start
Without Add-ons]

If so, enable add-ons one at a time until you find the add-on that is
causing your problem. Remove that add-on and replace it with a version
(from the publisher) that supports IE 7.

Any improvement after resetting IE 7 to its defaults?

[Tools  > Internet Options > Advanced tab > Reset Internet Explorer
settings > Reset button > close IE 7 and restart it]

Have you thoroughly scanned your system for malicious software with
/several/ of the better online scanners (Kaspersky, Eset, Trend Micro,
Panda, Sophos, Symantec etc.) and, if necessary, submitted a HiJack This
log to one of the expert web sites that analyze these logs?

---
Leonard Grey
Errare humanum est

You may have a horked (dirty; bad; flawed) install of IE7.  I suggest that
you..,

1. Uninstall IE7 (which automatically returns you to IE6) per
http://www.ie-vista.com/kbase2.html

2. Uninstall all toolbars and third-party Windows Themes (including Window
Blinds).

3. Reinstall IE7 per http://www.ie-vista.com/known_issues.html#pre-install,
and using http://www.microsoft.com/windows/downloads/default.mspx as the
installation source, not Automatic/Windows Update.

Also see:

IEBlog : IE7 (Un)Installation and Anti-Malware Applications
http://blogs.msdn.com/ie/archive/2006/10/11/IE7-Installation-and-Anti_2D00_Malwa
re-Applications.aspx

What's New in Internet Explorer 7
http://msdn.microsoft.com/workshop/essentials/whatsnew/whatsnew_70_sdk.asp?frame=true