Windows

Before it was completely removed, Motorola's site indicated a clean install (not an upgrade) of Windows XP is required to get the SM56 to function in XP; and, that once installed, the driver cannot be upgraded. The Windows 2000 driver should be usedfor XP.
This info is from http://808news.com/56k/sm56.htm
HOwever, I was able to loacte a page with a driver for XP
http://support.ap.dell.com/ap/en/filelib/download/index.asp?fileid=R35341&sid=DIM_PNT_P4_8100&lang=EN&lib=0&os=WW1&searchtype=filter
which is described as:
Dell Windows XP Drivers for the modem formerly known as Motorola SM56 Data/Fax

GOod luck