df wrote:PSP can only address up to 2gb of RAM. You could have a super computer with 1.2tb of RAM and still PSP would only access 2gb. Not usually a problem unless you're working on very very large files and have multiple layers, but for most normal uses it wouldn't be a problem until PSP doesn't give back the memory it used on an image. Eventually it runs out of RAM to use. The third party program link I gave earlier does correct this behavior, but if the program needs the RAM it won't give it back (which is good since if it took RAM that the program needed it would crash the program).
Other things you can do is go into your preferences and turn off Fast Redo on the Undo tab and possibly other things as well. In X4 there's also a scratch disk, make sure that's turned on and has ample space on that hard drive. Another thing that can help is looking up ReadyBoost for your Vista or Windows 7 (not XP or NT) computer and seeing if you have a memory card or USB drive that's capable of using that.
Dan - thanks - just returned home and about to do some images with PSPX4 - so we'll see if we can squeeze a little more out of my machine