Install as a Windows Service

First download the Windows 2003 Resource kit from the Microsoft site and install it.
Next, assuming that SABnzbd is installed in d:\bin\sabnzbd, do the following steps.

Run in a cmd window:

instsrv SABnzbd "c:\Program Files\Windows Resource Kits\Tools\srvany.exe"

Run in a cmd window:

install_service.reg || (content see below)

Set dependency, by running in a cmd.exe window:

sc config SABnzbd depend= Tcpip

Set a suitable user account for the service "sabnzbd".
Set the service "sabnzbd" to run automatic

Content of install_service.reg, create a text file containing:
(modify the path to match your setup.)

Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SABnzbd\Parameters]
"AppDirectory"="d:\\bin\\SABnzbd"
"Application"="D:\\bin\\SABnzbd\\SABnzbd.exe"
"AppParameters"="-d -f d:\\MyWorkDir\\sabnzbd.ini"

Doing this you can skip running startup scrips etc.