Lost access to Ext3 Partition

I've been running triple-boot Mac 10.6, Windows 7, and Ubuntu 11.10 for several months (okay, previous versions of Ubuntu included). I have a directory in the Ext3 partition (called /Common) where I put all the stuff I want to see from all three OSes. Today I cannot find that partition from the Mac, where I am now spending most of my time. I can see it okay from Windows, so I'm not panicking (yet). I've rebooted, and I've done the "Command-Alt-R-P" trick to try to restore everything.

How do I recover access to that partition? I can find no version information, but the date stamps on the registration app is July 31, 2011, and I haven't upgraded the software since it was installed.