I got the same problem today: task manager disabled, so I suspected a virus.
Luckily I had installed another process manager (TuneUp Utilities) so I was able to locate the offending process: RJKFFARG. Although that was the name of the process, it was mapped to WIN32.DLL in the windows\system folder.
As I am familiar with the processes that run in my computer, I killed the RJKFFARG and proceeded to restore the Task Manager through the registry.
Then I ran SuperAntiSpyware as suggested here, and it found Adware.Vundo-Variant/Small-A in the computer... And the related files were... RJKFFARG.DLL!
So now I'm sure this was the problem. I use SpywareBlaster, Lavasoft Ad-Aware and Avast! Antivirus...
This is the second infection that I get when using Avast. The first one was the AMVO virus... Can someone please comment on why Avast is letting this infections through?