maineman has summed up the Patin-Couffin driver nicely.
It is a CD/DVD access driver that allows software to "talk" to the drives.
And yes multiple apps will share the same install of the PC driver, having multi installs of it will cause problems.
When you install a program that uses the Patin-Couffin driver it will check if there is a driver already installed and what version it is, if it is an up to date driver the software will not attempt to install the driver.
26/02/2007 9:23:40 AM info Driver is up to date. No install is attempted.
26/02/2007 9:23:40 AM info embedded driver revision : 37
26/02/2007 9:23:40 AM info A driver has been found on the system. Internal revision 37