No, unlike Windows, there is no "roll-back". You will have to an Achive & Install (keeping the same User settings) of your copy of Panther and then upgrade it to 10.3.8 (download the update from the Apple website). You should also repair Permission from the Disk Utility of the Mac OS Setup after you are done downgrading.
By doing that, you will lose all your changes to the Library and System folders. Before you remove the "Previous System" folder make sure that you have grabbed everything you need from there (like Quicktime Codecs).
Or else just wait for Tiger (which is what I am going to do).