According to Adobe, Lightroom will not run from a catalog on a network drive. I've found this to be true on my Macs.... the catalog has to be on a local drive (I use USB 2.0 externals drives).
However, I have a friend using Vista who has his catalog and image files on a server drive, mapped to a local drive letter on his machine. He uses this setup with Lightroom with no problems at all.
So depending on your configuration it may be worth a try, but given that it's not officially supported I wouldn't expect too much.