I suspect that the settings are held in the Windows Registry - but where these are may be OS-version-specific, and the interpretation of the contents may also be dependent on individual drivers.
For example, on my Win XP Pro machine, I have a registry key
HKEY_CURRENT_USER\Printers.
This has several sub-keys, including DevModesPerUser, DevModes2 and Settings.
Each of these sub-keys has a number of REG_BINARY name/value pairs, one per logical printer.
But I don't know how to interpret the contents of the values; they are large binary fields, which appear to contains names in Unicode format; I suspect that each field may be a collection of TLD (Type/Length/Data) items (or LTD, or TLLD, or similar) but I don't really know.