We have followed up on this through the support channel, but I thought I would post the reply here too in case it's of help to anyone else.
Getting community extensions working on an x64 server is not supported out of the box, but it is possible with some manual modifications. Before you start, ensure you have a SQL instance available and IIS/ASP.NET installed on the server. In order to install the 64bit version of ASP.NET I ran this command line:
"C:\Windows\Microsoft.NET\Framework64\v2.0.50727\aspnet_regiis.exe -i"
I also had to then enable "ASP.NET v2.0.50727" in the Web Service Extensions section in IIS Manager.
Here are the steps to then follow in order to install Community Extensions Server:
1. Add a DWORD registry value "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Setup\OC Manager\Subcomponents\aspnet" with a value of 1.
2. Run the Community Extensions Setup - it should now complete, but the configuration tool will fail to start.
3. Copy the 2 registry values below "HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Innovasys\CommunityServer" to a new key "HKEY_LOCAL_MACHINE\SOFTWARE\Innovasys\CommunityServer".
4. Run the "Configure Innovasys Community Extensions Server" tool from the "Innovasys Community Extensions Server" Start Menu Group and go through the various tabs setting the options as required.
5. Once you have completed the configuration, use the "Diagnostics Page" shortcut from the "Innovasys Community Extensions Server" Start Menu Group to check that the server is responding ok.