You have at least three options. I have presented them in order of usage preference.

Method 1 - You can use the SC tool (Sc.exe) included in the Resource Kit.

Open a Command Prompt and enter

sc delete <service-name>

Tool help snippet follows:

DESCRIPTION:
        SC is a command line program used for communicating with the
        NT Service Controller and services.

delete----------Deletes a service (from the registry).

Method 2 - use delserv

Download and use delserv command line utility. This is a legacy tool developed for Windows 2000. In current Window XP boxes this was superseded by sc described in method 1.

Method 3 - manually delete registry entries

Windows services are registered under the following registry key.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services

Search for the sub-key with the service name under referred key and delete it.