I have had several reports, both confirmed and unconfirmed, of problems running JPEGView when certain system extensions are installed. It is important to note that NONE OF THESE ARE FATAL! They just mean that you need to take precautions when running JPEGView with any of the following software. Workarounds are provided for each problem, and if I can find away to properly resolve any of these conflicts, I will release a fix for it immediately.
OptiMem
--------
I have heard reports that early versions of OptiMem won't let JPEGView open images; you may get a "Not enough memory to open" error. The only real solution to this is to turn off OptiMem for JPEGView. I have also heard that if you run a slide show first, and then open your images, things will work better. Don't ask me why.
DragWindow II
-------------
This utility has a known bug in it that will prevent you from dragging JPEGView's windows around. There is nothing I can do to work around the problem; if you want it fixed, bug the DragWindow author about it. An annoying workaround is to always hold the command key down when dragging windows.