Running Mecury Mail as a Service
Mercury mail is a great, free mail server that can be used for dozens of things. Unfortunately the free version does not run as a a service.
This post will explain how to run the free version of Mercury Mail as a service. This procedure could be extended to run other processes as services as well.
Creating a Customer Service
Review the following KB article:
http://support.microsoft.com/kb/137890
In short, you can use Instrsrv.exe to create your own services and srvany.exe to start executables. Instrsrv.exe and srvany.exe are included in the Windows Server 2003 Resource Kit Tools which can be downloaded here:
http://www.microsoft.com/downloads/details.aspx?FamilyID=9D467A69-57FF-4AE7-96EE-B18C4790CFFD&displaylang=en
Both instsrv.exe and srvany.exe have worked for me on x64 Server 2008
Creating the Mercury Mail Service
Create a folder called service in your MERCURY installation folder. Copy instsrv.exe and srvany.exe. Create to batch scripts, call one service.bat and the other remove.bat. You should have something that looks like this:

Add the following to service.bat (this batch file will create the service)
Add the following to remove.bat (this batch file remove/uninstall the service)
Next run service.bat. This will create the service entry.
The final step is to setup the registry for srvany.exe. Create the following keys and values:

Finally start up the service.

Be careful not to start Mercury in the native app mode while the service is running, or you might make it angry. The best way to do it is to stop the service, launch Mercury, make your configuration changes, close Mercury, restart the service.
Conclusion
Hope you found this information useful!