LANMonkey
I do that by making a VPN connection to my SME server (from a remote Windows 7 workstation). Then select Run, enter the Windows server name eg //windowssvr and then right click on the connection name (windowssvr) & select Remote Access connection (or similar name), login & I have the Windows server desktop displayed.
I would ask, why do you want to use a Windows Home Server (WHS) when you have a much more secure SME server as web server (using Apache) ?
ProxyPass does not work for local users trying to access the site, it only works for external users.
Also the URL used in the proxypass db setting should have a trailing slash ie
http://symbiota.homeserver.com/Refer to the FAQ.
I cannot recall exactly now, but there may be some issues with that UPnP protocol requirement, so do some reading, search google ? Note I do not have any issues with UPnP when using VPN.