There is a folk at TÚAW writing an article explaining how to enable inertial scrolling on the old glass trackpad MacBook Pro. The result isn't successful. Here is some background that why it fails.
Inertial scrolling is a new feature that appears on iPhone, iPod touch. When the scrolling occurs, there is a momentum left after the fingers are raising from the trackpad. This feature is currently available on the MacBook Pro, and MacBook which released after April 2010.
After an investigation, it turns out that the new model also contains new trackpad. The old trackpad product id is 0x236 but the new one is 0x237. Driver versions are also differences. The old trackpad has 0.77 but the new one has 0.90.
Such a simple hack as describe in the article isn't enough to enable that feature. An updated trackpad preference pane and the new driver for the old model are also required. I hope 10.6.4 will enable this feature.