There are many things that contribute to slow loading of pages.
Server. Maybe full or too many users accessing the one server at any given time
PC you are using - Modem Speed 56k it happens a lot to be quite slow..
RAM on Computer
Amount Free Space on the Computer
What Browser you are using. IE can sometimes tend to be slow. Netscape on the other hand is fast as long as the HTML on the otherside is correct and not needing to be fixed.
There are a few more reasons but they are the main ones and mostly always contribute to what you are experincing.