A quick something that nbody else seems to have mentioned here. You say that you use a dial up connection right. Unless you have a fixed IP (can you do this with dial up?) then your IP address will likely change every time you connect. I would say that it is possibly some kind of malware installed on your end (as do most other people by the looks of it).
Also, this will probably be a bad suggestion, but has anybody considered some type of hardware problem? If it persists with a clean install could this be a possibility?
If everything looks perfect, then there is something you don\'t know