Can you maintain a Modem connection for an in defiant time without using PC Anywhere? If you can not I would start to look at the phone wiring as a first option.
I've seen some really nasty things done in place that new business have moved into or an existing business has expanded into. In one place they had a bank of 5 2 socket phone lines and one had an ADSL connection plugged in. They where advised to take out the working ADSL and try that modem on the one that wasn't working and when that didn't work they returned the working one to the original location and it no longer worked. Only took half a day to find out that the line that the filter was plugged into was not the line that the ADSL connection was on. :D
As none where marked and I didn't pull the DSL Modem I was the one who got the job of fixing it.
Col