Server service is set to automaticly start if, under the properties of your network connection, you enable "File and Printer Sharing.'
That triggers the Server entry. You can find clients where only 'Client for Microsoft Networking' is enabled, that triggers the Workstation service.
You often find clients that under TCP/IP, properties, Advanced, WINS tab, that there is not a check mark next to 'enable Netbios over TCP/IP'. That checkmark enables the Netbt Helper Service.
Many of these services are dependent. XP by default will try and add the "Client for Microsoft Networking" and "File and Printer Sharing" as a default. It does not make the extra step to 'enable Netbios over TCP/IP' as a default. I have lost the argument too many times with MS product groups on this issue, it is not going to be enabled as a default setting.
Someday I will sit down and write a smalll local DNS server for XP and end this issue once and for all. Ask me again at the end of April, 2004 as this is high on my list of issues for the MS product groups at the MVP summit.