Hi,
Which version of Windows?
Which version of Internet Explorer?
Do the troublesome pages have anything in common such as Flash, Java
applets, JavaScript?
Did you install or update a third-party program (security, privacy, etc.)
just before the problems started?

Assuming IE6/XP SP2 (or SP3) or IE7...
1. You may have an incompatible browser add-on.
See: http://www.enhanceie.com/ie/troubleshoot.asp
for troubleshooting information.
More at:
IEBlog  Troubleshooting and Internet Explorer’s (No Add-ons) Mode:
http://blogs.msdn.com/ie/archive/2006/07/25/678113.aspx

2. With the warning that a reset will delete autocomplete data, such as
passwords and you will have to reinstall browser add-ons, work through this
article:
936213- How to optimize or reset Internet Explorer 7:
http://support.microsoft.com/kb/936213/en-us

3. This may be a malware problem- adware, spyware, hijacker, trojan, etc.
See these sites for help:
The Parasite Fight http://www.aumha.org/a/quickfix.htm
Dealing with Unwanted Spyware and Parasites:
http://mvps.org/winhelp2002/unwanted.htm
Malware Removal and Prevention Overview - CastleCopsWiki:
http://wiki.castlecops.com/Malware_Removal_and_Prevention:_Overview
Bugs, Glitches & Stuffups: http://www.mvps.org/inetexplorer/Darnit.html
Removing Malware:
http://www.elephantboycomputers.com/page2.html#Removing_Malware
827315- Unexplained computer behavior may be caused by deceptive software:
http://support.microsoft.com/default.aspx?scid=827315

Hope this helps,
Don
[MS MVP- IE]