Try a repair of IE....
Reboot to Safe Mode
Go to Add/Remove Programs and try a repair of Internet Explorer from there.
Go to the entry for 'Microsoft Internet Explorer 6 SP1 and Internet Tools'
in Add/Remove Programs
Click on Remove - and click on Repair on the window that pops up
Reboot on request to Normal Mode

If the above entry isn't there, you first need to uninstall all the patches
applied, then do the repair, then reapply the patches
The patches are listed in Add/Remove under the names 'Internet Explorer
Qxxxxxx'
highlight, click Remove - reboot if requested.
Repeat until the MSIE6SP1 entry appears - then repair as above.

HTH