If you use a premium anti virus suite, go to the manufacturer site and search there for "Diallers"
Also try the free programs Ad aware and the Microsoft Anti Spyware program. The latter contains a useful suite of tools (very intuitive) to see what progs are called during start up and what progs are currently running. Very useful - and free too.
If you have a rogue dialler, it is probably trying to dial an 0900 or foreign number. Get BT to put a bar on these two types of number - and do tell them that you are having dialler trouble. They have been implicated themselves in recent months (as carriers of an unauthorised "transaction")and now are a lot more helpful in trying to stop it than they used to be, if my experience is anything to go by. Best bet, is to unplug the modem, but if you are using fax, then it is the lesser of two evils I suppose.
Conan