Aerbabe - a paranoid thought! There has been a fair bit of 'hijacking' of the Freeserve DUN lately (covered on this forum and in the UK press) which diverts to a premium rate number at vast expense to you. I ASSUME you have looked at the settings for the Freeserve DUN to check?
In W2000 it is in 'Start'/'Settings'/'Network and Dial-up Connections'