You need to download the new camera raw. But, it won't work with CS2. So, download it and use the stand alone DNG converter.
Convert on your desktop and import to your program. CS2 may not recognize the file and then you have to feed Adobe for the upgrade...
I don't recall the exact details about CS2 and the G1 DNG files. But this is what I would try (I have now updated my Photoshop and uninstalled the old version so I can't try it it, again):
Download the Adobe DNG converter Streetshooter mentioned. Put a G1 raw file taken with a Panasonic lens and one taken with a manual adapted lens in a directory to test it. Start the DNG converter and check the settings. What you need is to find what output version of the DNGs that can be handled by Photoshop and Bridge CS2. Start with DNG v2.4, go to v4.1 and so on and see what works for you.
You'll find that the older versions of the DNG format make for huge DNG files if you have used a Panasonic lens when shooting. That has to do with the "problem" introduced by Panasonic by adding the lens correction data to the raw files and it took some time for Adobe to include these data and still being able to compress the DNG file (or keep the raw format technically speaking). 45MB files... not funny. The DNGs from adapted manual lenses will be around 12MB as expected.
Let us know if you succeed or if you need more ideas, OK?