If a program doesn't buffer a 24-bit or 32-bit color image properly, Windows NT will slow down greatly. If your system paints the screen slowly or overworks the disk paging file, switch to a lower color setting and you will see drastic improvements.
Part of the problem could be poor program design. My experience was testing a custom plotting program. I had Delphi, the plot program and Windows Paint loaded in 16 MB of RAM. This stressed the system quite a bit. The disk started to thrash and the display would update slowly when I switched between programs. Borland includes an object called Image in their Delphi programming environment. It can be used to store and display various image formats. This object takes a brute force attack at image storage and is not optimized to quickly display the image as the major image programs (Photoshop, Corel Paint) are. Perhaps if I wanted to spend more $$$ for a better set of image components it would run faster.
My opinion is that Windows has display problems when virtual memory runs low. Both Windows and Macintosh Quickdraw leave much up to the application when the screen must be refreshed. If a large image must be copied or fit into a rectangle on the screen, much image memory must be accessed. In 16 or 256 color mode the memory involved isn't much and the program performs well. When running true color, the larger amount of memory required causes too much disk thrashing when memory is low.