I mentioned "sharing" a catalog between two computers a little over a week ago. Some Windows users haven't been able to get this to work for them. When you map network drives, Lightroom won't use the catalog. Typical Adobe problem. That doesn't stop us old-school DOS geeks. Instead, you have to use the old MSDOS SUBST command in a command line. Lightroom doesn't see that as a mapped drive, even though we're doing the same thing ;~). For example, if you have your data on network drive X: and your catalog on drive Y:, create a Batch script to reassign those locations (text file with a .BAT file extension). In my example, I'll reassign them to M: and N: (obviously, substitute the right drives for your system). Call the text file you create to do this LRMAP.BAT:
LRMAP.BAT
==============
REM >> run on startup to assign data drives for LR
SUBST M: X://
SUBST N: Y://
That's it. Just add LRMAP.BAT to your startup items. You now can access the data on drive M: and the catalog on drive N: from within Lightroom on both computers. Just don't try to do this simultaneously ;~). (Tested on XP, but not Vista or 7.)