Re: X crashing at startup after update
The content of /lib/modules/2.6.15-27-386/volatile/ is provide by Ubuntu. The 'volatile' part means that it isn't static, and does not survive a reboot. That's how Ubuntu has chosen to ship their packaging of the nvidia X driver.
Since you're reporting stability problems, I'd suggest retesting with the 1.0-9626 driver, as well as verifying that you have the latest BIOS for the motherboard.