Time Machine will be available with Leopard, but for those of you itching to get your hands on it you can set up TimeDrawer on your Mac. This application, accessible from the preferences pane, lets you make backups of your files and go back to old versions, not matter the number of changes you've applied to it.
The application offers two browser views, a more traditional window style and a widget like illumination view. We really like the side scrolling in the latter view, as it clearly shows you the different versions of files and when each one was saved.
One minor little drawback with it is that it tends to pop up every now and then for no reason.
TimeDrawer lets you apply rules to filter through your files and you can adjust the size of your database to save backups and when records can be deleted.