pretty much back up any files on your hard drive that you wish to keep. unplug any ipods, firewire hard drives, etc. in fact, anything other than a keyboard and monitor and mouse, unplug.
pop in your tiger os install disc, restart, or whatever gets it to boot, do a CLEAN install, the one that will wipe your drive clean, and reinstal everything from scratch.
note, this will DESTROY everyting on your hard drive, backup everything you want to keep.
then, i usually run all the OS updates, then install FCP studio, then install all the updates, rebooting and restarting when it asks me. then I go and install all my other software, photoshop, squeeze, keynote, ilife, etc.