Hey Shrimp,
Funny, I am in almost the identical situation except I have Eircom Broadband as well as the Phonewatch...
My broadband was so weak it used to drop me. I spent hours onto their support and finally they sent me a new modem which has sort of helped but the best I get is "Good" signal - again, my desktop at home in the same room works fine. When I am downstairs with my laptop i have excellent coverage.
I have heard of a signal booster that you can put in the office, which should boost the signal, but dont know much about these or where to install it - do i also need a phone connection for this?
Sorry to piggyback your post but I have the exact same issue...