A multi-user version of Lightroom would be very useful, but it is currently resolutely single-user. I believe this is a result of it using SQLite as the underlying database instead of the full version of SQL. Trying to batter it into submission will give you endless headaches.
The only way round it is to have a main catalogue and let your multiple users work on sub-catalogues. But there is no built-in way to track changes to individual images between catalogues, so you will need to develop a suitably disciplined workflow system outside of LR.
If you have multiple users working on the same images, I'm afraid you're going to find it very difficult, but if the users are working on separate images, you should be able to make it work. The tools are export/import as catalog and using xmp data written to xmp files (raw) or to the image files (tiff, jpeg etc). If you do the export/import catalog, LR will just overwrite the metadata in its database, or create multiple virtual copies (depending what you tell it to do). If you use the metadata on individual files, you can set it to flag files where the metadata in the file/xmp is different from the metadata in the catalogue, and it will tell you which is newer - but you have to decide how to synchronise it - and that's down to having a foolproof workflow system in place.
Good luck! Come back and let us know how you get on, and don't hesitate to ask if you need more help.
Patrick Cunningham
