100% CPU usage by rundll32.exe

I have been afflicted with the 100% CPU usage problem. Rundll32.exe is usually at 100%. This most likely happens when I start browsing the internet. When I first turn on my computer, everything is fine, but then it starts to lag when I start browsing. I suspected it was a trojan and followed Majorgeek's tutorial for cleaning up viruses and trojans. Adaware and Spybot detected nothing. How should I fix this problem? Let me know if you need more information.

 

Ad-Aware and Spybot generally are used to clean out spyware or adware. Have you run a virus scan with updated virus definitions?

 

I have run the online TrendMicro virus scan and Norton Security Check. I could still run my own Norton Antivirus, which is updated. By the way, here are my computer specs:

Thinkpad T41
1.60 GHz
512 MB RAM
Windows XP, SP2

 

I have seen both run32dll.exe and rundll32.exe and they could both be spyware or a virus. I had the same problem at one time and a virus scan worked. Maybe try the scan in safe mode? Is there more than one rundll32.exe in the process list?