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?

Did you install IE 7 (sorry, I don't remember)? If so:

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.

---
Leonard Grey
Errare humanum est