What is the exact error message?

Using SFC Extract a fresh copy of RUNDLL32.EXE from your Windows CD or Cab files on
the drive if present, usually in c:\windows\options\cabs, and place it in the Windows
folder.

To extract a file using SFC:
Start > Run, type in:  sfc  and press enter.
Place a tic next to "Extract one file from......"
Type in the name of the file and click Start.
Browse to or type in the path to where the file is being restored from, the Win98
folder on the CD or where the .cab files are on the drive.
Browse to or type in the path of where to save it.
Click Ok.

**It is pertinent to run the update for each program before running to be sure you
have the latest definitions.**
Download/run Cool Web Shredder from:
http://www.spywareinfo.com/~merijn/downloads.html

For Info on Cool Web Search Variants:
http://www.spywareinfo.com/~merijn/cwschronicles.html

Then download/install/run Ad-Aware to detect/rid of any other parasites/spyware that
may be installed. It can be obtained free from:
http://www.lavasoftusa.com/
After installing Ad-Aware, open it and click on the ref update to get the latest
up-to-date ref file, then run Ad-Aware and delete everything it finds.

And/or download/install/run:
Spybot - Search & Destroy:
http://security.kolla.de/index.php?lang=en&page=download
Run it at it's default settings until you learn an know more about it.

If you still have problems, download/run HijackThis from:
http://www.merijn.org/
Do not remove anything with it until you get advice on what to remove, HJThis will
list many apps that are needed along with the bad ones. Read the quick start here on
how to create a log file that can be copied/pasted into a forum that can provide
assistance on removal of unwanted pests.
http://mjc1.com/mirror/hjt/#quick

Then post the logs to an appropriate NG here where they specialize in
spyware/hijacker removal:
http://forums.spywareinfo.com/

It's also a good idea to have a HOSTS file to block bad sites, scroll to HOSTS File
Manager here:
http://www.mvps.org/PracticallyNerded/Software.htm

Another good app is SpywareBlaster which stops the badboys before they even get a
chance to install:
http://www.javacoolsoftware.com/spywareblaster.html