For Windows 2K/XP only.
Until a Web interface appears for the serverloader, this simple utility will allow you to remotely control your server - it works fine for me anyway.
Link to PsExec web page with download
I've used PsExec to start/stop my HLDS server and do other things, and it seems to work just fine.
The really nice thing about PsExec is that you do not have to install anything on the server, however be aware that PsExec will install and execute a service on the remote machine automatically for you.
Here's some more info on the utility