Marc Moini has updated SmartScroll to version 3.6b2. SmartScroll offers proportional scroll bars and live scrolling on System 7 on up. The change include Mac OS 9 compatibility and other new features. According to Mr. Moini:
Apple has now adopted 'Smart Scrolling' in Mac OS, but only the original Smart Scroll brings Proportional Thumbs and Live Scrolling to applications such as Netscape, Emailer, AppleWorks, Word, and most system add-ons such as control panels.
Version 3.6b2 now also allows adjusting Scrolling Speed to user-selected rates, for comfortable scrolling on all Mac models. Support for Mac OS 9.0 is featured as well.
Smart Scroll runs on Mac OS 9.0 and previous versions (going back to System 7.0). It is shareware, so you can try it for free then buy only if you like it. The shareware fee is $12, registered users of previous versions may upgrade for free.