Have you tried Spybot or Adaware programs to see if they detect and can delete it? Be a bit careful with this one Tosh because it dials international numbers, not internet numbers (ie local call rate or freephone).
Hit ctrl, alt and delete at the same time and see if the program pdialer.exe is running. Click once on it and select end process and see if that kills it temporarily.
Sorry to say that this is usually installed from Porn or Warez sites and is normally done by popping up a box with any text on it which you OK to close.
To prevent things like this happening again, set your internet security level to medium or greater in tools, internet options, security menu. Any probs, let me know what browser and operating system you have (for example IE6.0.2600 and Windows XP Pro etc).