I too have been experiencing the Lightroom Not Responding issue. I am running LR 1.0 on a Windows XP SP2 machine with 2 Gigs Ram and a good processor. I have important only 1,000 pics or so, but for some reason in the middle of a session it just starts locking up.
I *really* wanted love this program. I like the UI and while it is missing a few minor features, it is really a good program, but until this gets addressed -- i.e. LR 2.0 -- I am going back to Bridge/ACR. Sigh.
It is most likely something on your machine that is causing this. I have a similar environment and its been running fine for me... have about 13k images in the database. I am on a Core2Duo XP box with 2G of ram. I have 100% of my images on a NAS box over a GigaE network, and the database on a SATA drive other than C:. Try to make sure you have everything else turned off on the machine.