Hi there i have found two different solutions to this very common problem
as LR dont let you merge databases so far.
Please note that these solutions are not mine and i still havent had time to try them. Use them at your own risk.
Solution 1
"Adobe Lightroom synchronized on different Windows XP machines
Here is how I am able have the same Lightroom working environment on different Windows XP machines.
There are three requirements. First, that images are stored in a folder tree and that the folder tree is synchronized on the different machines. Second, that the Lightroom library folder tree and the Lightroom settings folder tree are synchronized on the different machines.
On my systems, the Lightroom folder tree is within the images folder tree, and the Lightroom settings folder tree is
C:\Documents and Settings\Dan\Application Data\Adobe\Lightroom
I use Second Copy 7.0 for one-click synchronization, and there are various other tools that do this.
The method has three parts.
• First, define a Desktop shortcut with the same name (Images, say) on each machine, and point this shortcut to the root of the image folder tree on each machine.
• Second, set Lightroom to prompt for the database location on startup, so that it finds the database on each machine.
• Third, reference images in Lightroom using the shortcut to navigate to desired folders on the image folder tree. Thereby, Lightroom (evidently) records a given image as being at the same logical location on all machines, while Windows XP resolves the logical location to actual location through its shortcut mechanism.
Here is an example. The root of my image folder tree is D:\Photos\ on an internal disk of a workstation, and Z:\Photos\ on an external disk of a laptop. The Desktop shortcut on each machine is named Images, and it points to D:\Photos\ on the workstation and to Z:\Photos\ on the laptop. With this setup in place, when I import files into Lightroom (by reference), I navigate to them through the Desktop shortcut, as Desktop:\Images\.... For example, when I point Lightroom to the image folder
Desktop:\Images\Canon 10D\Pomfret
the location is resolved by Windows XP to
D:\Photos\Canon 10D\Pomfret
on the workstation, and to
Z:\Photos\Canon 10D\Pomfret
on the laptop.
So far, this scheme has been working without any problems. It allows me to work with files on one machine, synchronize my image folder tree and Lightroom settings onto the other machine (by a single click to Second Copy 7.0 on each machine), and then continue working on the second machine where I left off on the first machine.
By the way, a very important benefit of this way of working is that all work is replicated on two different machines, and so if one machine fails, work can immediately continue on the other machine, with loss limited to the last synchronization.
On Mac OS X, the equivalent of Windows XP shortcuts is aliases, and the two approaches are described together at Aliases vs. Shortcuts. Presumably an analogous procedure can be used on Mac OS X machines.
I hope this way of synchronizing Lightroom on different Windows XP machines is helpful. I will be grateful for any suggestions for improvements or cautions/gotchas.
Solution 2
Here is a link to it as it is rather long on Adobe LR forum.
http://www.adobeforums.com/cgi-bin/webx?14@@.3bc340dc/2