first you have to create an oracle service.
u can use oradim to create the service with autostart option or control them with netstart.
[b]quoting orafaq[/b]
How can I automatically start Oracle on NT/2000?
To start a database automatically when your server boots up, ensure the following registry setting is enabled: ORA_sid_AUTOSTART. 
One can also specify autostart when creating new database services. Verify if this was done by opening Control Panel -> Services (Control Panel -> Administrative Tools -> Services on Windows 2000) and check if it is set to AUTOMATIC. 

You may need to recreate the services mentioned above using the "oradim" (Instance Manager) utility. Start by opening a DOS command console window. Look at this example (assume a SID of TEST): 

         rem Delete the old service
         ORADIM -DELETE -SID test -SRVC servicename

         rem Create a new services with the STARTMODE AUTO property
         oradim -new -sid TEST -intpwd ORACLE -startmode AUTO -pfile C:orantadminTESTpfileinitTEST.ora