what version of windows?
regardless, first of all if you are on dial up,physicaly disconnect the computer from the phone line.if you have broadband dont worry too much it cant dial out.
next restart the computer in safe mode,as soon the computer is turned on,keep tapping F8 and when the list of choices appear choose safe mode.
once windows starts it will look a bit strange,dont worry its like this in safe mode because it starts windows with minimum programs and drivers running.
click start/search or start/find and type in the name of the dialer ie/ "xxxmpeg" or whatever its called and click ok.anything found delete it.
once you have done this click start/run and type "regedit" click "edit/find" and type the dialers name in here too and click ok.if it finds anything it will stop on it and it will be highlighted.right click and delete then tap F3 to continue searching.keep going as before untill windows tells you its finished searching through the registry.
next if you have xp,click start run and type "msconfig" and click ok,click the start up tab and if there is any reference to the dialer here untick it and restart the computer.
that should work i think.