I am running Fileman from 1 virtual domain currently. However, I am the admin for 4 othe domains on this dedicated server. If I currently have it running under 1 user:group, but I have 3 other user:groups, can I just change the owner:group to my admin:admingroup and be able to manage the files in all 4 sites?

Such as:
/home/site1/www/fileman/file.cgi site1:site1
/home/site2/www/index.html site2:site2
/home/site3/www/index.html site3:site3

Where admin:admin could manage all of these, but only site1 actually has it installed.

If your host uses suExec, you will need separate installations in each account. You can always modify the templates to include links to the other accounts though.

Regards,
Charlie