I don't think its likely to be a fault between the modem and XP pro because my PC has XP pro and had a cheap Intel modem and ran it no bother, speeds of 47-50k. I wonder how the modem is set, are you positive its using the right driver? Are you using the modem driver disk which came with the modem or are you allowing XP to use its own driver. My Intel modem just used the XP pro driver and ran perfectely. The only other things I can think of are the Aries modem is faulty or something about the design of it doesn't like something about your phone line or theres a problem between the motherboard and the modem. Considering Savastore build hundreds of these and presumably haven't had a problem before I would be inclined towards the incorrect driver being installed or something wrong with the modem.