Moving images from one catalog to another

I have a large catalog. A VERY large catalog. It contains images from an event that runs every weekend for about two months, and it happens over an area of about 100 acres, with several stages and other performance areas. There are also shops. Anyway, may catalog is about to exceed the size of the hard drive it's stored on, so I thought I'd move some of the images to another catalog, and get them off the drive they're currently on. What's the best way to do this?