i think they meant they dont know how to support winXP if he had technical problems with it. they probably have had training in certain OSs and know how to deal with those specifically, but XP is different than MS other OS and to tell someone at the home what to click on without the little manual, it would just be too difficult for all. some might know, but not all.
adsl works just fine with winXP both home and pro. the minor problem that i see is that the install disks wil not work so the network will have to be sset up manually. no problem if yu know what you are doing, but recently got several calls from different friends trying to do the same thing with adsl and a network with winXP. it is actually very easy to do with a minor knowldege of tcp/ip.