A life-saving trick I learned about In Design CS 5.5:
My file (very large) was running SO SLOWLY.
I was about to give up.
Then, I hid my pages window.
As long as my "pages window" is hidden, the file runs super fast !!!!
.. or disable the continuously live updating thumbnail previews. That way you can still use the Pages panel for its regular functions.
Just turn off the thumbnail previews.
Might also be time to think about upgrading the hardware.
My computer should be plenty fast, no ?
How do I turn off thumbnail previews? or "disable" them?
Uncheck "Show Thumbnails" in the panel options.
And that's a pretty old box. It's probably the video card that's the bottleneck.
Open the pages panel menu and choose panel options.
I would certainly be thinking about moving to a more modern operating system.