That error message usually means either:
1) There is a networking problem ... make sure the IP address and subnet mask are correct. Best way is to let SME do the DHCP for your network unless your ADSL modem/router has to do that. If so, use static IP for each PC and use a HOSTS file on each PC. They go in:
Windows 95/98/Me -  c:\windows\hosts
Windows NT/2000/XP Pro - c:\winnt\system32\drivers\etc\hosts
Windows XP Home - c:\windows\system32\drivers\etc\hosts 
An example hosts file is:
# For example:
#   ip address   machine       comment
#       38.25.63.10     x.acme.com              # x client host
127.0.0.1       localhost
192.168.1.1   smeserver   # file server   
192.168.1.6   phantom      # Jim's PC
192.168.1.4   dianapalmer   # Diana's PC
192.l68.1.100   PRINTER      # Printer Server
2) Next most likely problem is a mis-spelled domain name. Make sure the domain name on the SME server is the same as the domain name you are try to connect to on the XP. upper/lower case may be a problem, but I forget ....just use the same in both.
Hope this can help.
Cheers
Ian 
