Win XP non winmodem buy recommendation

Hi, i want to test replace an older internal USR V.92 Fax Winmodem that a WinXP SP-1 user is complaining about disconnects with. gets them every minute or so. another consultant supposedly has gone over ISP settings with fine tooth comb. Speed set at 56K. the phone line has been replaced and works fine on other pc with different modem. No model number on the current winmodem is available to me right now. I am going to customers with several external USR modems: 33.6 Faxmodem, 56k Faxmodem and Courier to try. I am checking the HCL for them right now, www.usr.com says they are compatible…
My question: if I confirm the existing modem is the problem, what do you like for internal, non-winmodems for Windows XP? Thanks in advance.