If you have a wheel mouse, click the wheel like a button. Then move the
mouse cursor downward a little. The further you move it, the faster the page
scrolls.
This is a function of the mouse driver, not Word. There may be some
third-party software that can do it without a wheel mouse, but a short
Google session turned up that kind of software only for e-books on Palm
devices.
In Word 2002 it's the Autoscroll command. I don't think there's a
default shortcut key. Either assign it to a shortcut key or drag it
to a toolbar (Tools>Customize>All Commands>Autoscroll).