Windows 7 My Documents problem

Hi, I posted this in the general section a few days ago without luck, hope
it's OK to repost it here.

I have server 2003 with xp clients, running ok for 5 yrs. My documents
folder for each user is set to U:\ which is their home drive (typically
\\Server\UserName)

I have a new laptop with Win7, installed it & updated to latest patches as
local admin.

Made member of domain & logged in as one of my users. Wished to change the
my documents folder in same way. Found it in its new location
(C:\users\username\my documents) & went to the location tab. It shows as
\\Server\UserName\Vista !
It will not let me change it.

Can anybody explain what I am missing ?

TIA

Frank