You may want to read the MSDN articles:
"INFO: Running Visual Basic Applications as Windows NT Services" 
"NT Service: An OLE Control for Creating Windows NT Services in Visual Basic"

Here are some links to check out:
http://support.microsoft.com/support/kb/articles/Q170/8/83.asp
http://support.microsoft.com/support/kb/articles/Q175/9/48.ASP
http://msdn.microsoft.com/library/techart/msdn_ntsrvocx.htm
http://vbwire.com/advanced/howto/service2.asp
http://vbwire.com/advanced/howto/service.asp

