Would it be inconvenient to map it as a network drive instead?
Sometimes Windows is more “friendly” to network drives.
try logging on like this (may or may not work)
IpaddressOfServer\UserName
is this setup as a domain controller?
whether it is or isn’t, (if the above fails), try
ServerName\UserName
I’ve never had this problem with XP but I have had it quite often with vista.
If this doesn’t work, can you post your SMB settings for all four tabs under settings?
Sorry if this doesn’t help,
Robert