Answer:
You need a decent computer with at least 2gb of RAM (check your program requirements, they may have changed); 2gb may not be enough depending on image size/resolution, and amount of layers you are working with. On anything less than 1GB it will run slowly and crash from time to time. Photo editing programs are very memory intensive, the best system is one with lots of memory. The more layers you are working with and the larger the image is, the more memory your image editing program will consume. A good video card will also help out, however, it is the memory that is mainly important.
Good examples are computers are Mac Pro , and Dell Alienware M15X (there may be better examples at this time), but you can also have your computer custom built to meet your needs.