For the longest time, I had an unusually long delay in opening pictures in Windows XP with the built-in Picture and Fax Viewer. My computer had adequate memory, so that wasn't slowing things down. I tried defragmenting the hard disk, and doing a disk cleanup, but the problem persisted.
For awhile, I gave up on fixing it until recently when I found a solution in this discussion thread.
According to h41cyon, what is happening is that there are dead shortcuts in the same folder as the picture. (When I say "dead" I mean the shortcut is pointing to something that has been moved or deleted) Picture and Fax Viewer was delaying bringing up the picture because of these dead shortcuts. Delete the shortcuts, and the problem is solved. Guess what? He was right! Thanks h41cyon!