This screencast will show you how to transfer photos between different Lightroom catalogs, and it will go beyond that by also demonstrating how the whole process could be made a LOT easier if Adobe wanted to.
In the screencast, I refer to an article I wrote a while back, entitled “The next stage for Lightroom“, where I put forth a proposal for improving the way Lightroom stores photos, with an eye on catalog portability (laptops, for example). If you have the time, please read through that article after you see the video.
The video is about 10 1/2 minutes long, file size is 78MB, and it’s 720p HD, MOV. You can view it online by clicking on the screenshot below, or download it.