Hi Joel !
I had the same issue as you. My workflow based on P2 Duell Adapter and my Mac Book Pro was messed up after upgrading to 10.6. Here is my solution.
After few weeks using the USB (so slow) connexion of my HPX 171, I made a 20 Gb partition using GUID on my Mac Book Pro internal HDD and installed Leopard on it (with Panasonic P2 drivers for 10.5).
On the field or at the office, when I have to ingest my P2 content in my workflow, I boot (or re-boot) my laptop with Leopard using the boot function in the System Preferences. Then I plug the Duell Adapter and insert my P2 card and import all my files on a dedicated partition or on an external LaCie Rubbed hard drive using FW800.
This works perfectly !