Unlike Windows, Linux does not seperate the drivers from the rest of the kernel tree, so the version of the driver is (in most cases, at least) the same as the version of the kernel on your system.
Some drivers do use their own versioning system, but this is only really of interest if you are developing the driver. In which case, you will find it in the kernel source files. Also, some manufacturer-supplied drivers are distributed seperately from the kernel for legal reasons (your ATI driver probably falls into this category). Normally, there's an RPM installed for these drivers, so you can get the version number off the RPM package information, using your distro's configuration tool or the rpm command.