I don't know of a way to reduce the size of the pasteboard. If you go to View menu and select Actual size, Fit page, or Fit Spread, you can resize the window to show less of the pasteboard.
Generally, slowness is tied to several things and your machine's display RAM and cpu RAM. The more in each the better. Try going to View menu/Display Performance and select either typical of optimized and see if that speeds things up. Pics might not look pretty with those settings but that's only screen - not print quality.
You can also go to ID prefs/Display performance and play with the sliders to speed up refresh while decreasing the view quality of certain types of images.
If you have a lot of graphics - as opposed to pure text - in a 200 page doc, things are going to get slow unless you have a lot of RAM and a good video card. One trick is to break it into several docs and then merge them later via either the Book feature or by using the Pages pallettes to drag pages from one doc to the next. The do page numbering, etc.
Using OSX 10.3.9 on a G4