Installing RH over a server is a definite no-no. You'll have to have an additional RH licence to allow both of you to use it at the same time. Read this link to understand the difference between RH Server and RoboSourceControl. You definitely don't need RH Server although you could use RoboSourceControl (or another source control product). That would ensure two of you could not edit the same files at the same time.
It sounds to me like you need to have a merged project setup. One project would have the content that the same in both documentation sets. You could each have another project that would include the merged content. This would work regardless of your output. For example you even produce webhelp and the other person output to a PDF if you wanted. If you are producing merged webhelp you do best to check out this link first.
Read the RoboColum(n).
Apart from what Colum suggested, you can use a source control application to 'single source' your files. I use MS VSS and to 'single source' the file, I link files (using the same file within different VSS project) within VSS. I use a simple batch to get the latest version of these files for all projects every morning.
Changing the file from any project will change the file in the source control database. Just getting the latest version in all projects, synchronizes the files.
Great, thanks for the responses.
I think I'll try and get another licence or at least a trial set up on another machine and test this out.
Think it will turn out that I will control the files that the other user may want to use, without them needing to make any changes. So source control might be the simpliest way to go.
time for testing.