Generally, you can just install over the top of existing drivers.
If you aren't confident, use the uninstall option in setup then install new drivers.
If you really aren't confident, uninstall, reboot in safe mode, run driver sweeper, then install new drivers.
Personally, I had to use driver sweeper for the first time after installing 10.6. 10.6s are giving performance issues it seems.
IMO, 10.3 or 10.4 seem to be most stable ATM.