Not sure about windows, But I think best bet is to get a cheap box, doesnt need to be anything special something cheap and old like a PII 400mhz and set linux up on that, cos the problem with using it in your current box is that itll probably lag it quite a bit when other people have access to it,

I think thats your best bet,

You want to try searchning for things like "dial in daemon windows" or "ppp daemon windows"

i2c