Nobbyhigo, you don't say whether you have a broadband connection or a dial-up connection. If you are on broadband, then dialers aren't anything to worry about.
If, however, you connect to the internet over a dial-up connection, it would be a good idea to download and install AdAware SE click here and Spybot Search and Destroy click here
Both of these are Windows compatable and scan your system for dialers and other types of spyware. These will happily both run on your system and what one misses, the other will pick up. Anti-virus software doesn't check for spyware, that's why you need spyware scanners.
Like anti-virus software, it's important that you regularily check for updates. If you visit this forum on a regular basis, forum members will often start a thread informing other members that an update is available.
Even if you are on broadband, it's advisable to have this type of software on your system, as there are other types of spyware that can get on your system that can cause problems.
If your unsure about anything, post back and someone will try and point you in the right direction.
Hope this helps, dagwoood.