What options exist when the vendor does not supply an ADB driver for an Android device? I bought an Android phone and the vendor does not offer any drivers whatsoever. The Android SDK and the drivers that come with it don't seem to work with the device, but the device itself reports as Android 2.2.1. 

Other users have reported that the drivers of the Nook Color worked for them, but I cannot confirm this, after trying.

What options do I have to connect to the device (and ultimately to root it)?

Is it truly just the .inf file that I need to manipulate in order to make the device ID known to Windows? After all there are tools to figure out those strings while the device is connected (although "unknown") ...

The model in question is a Simvalley SP-60 GPS.

Note:
The OS I need drivers for is either Windows 7 x64 or, if anyone has successfully done that, Windows XP 32bit (under VMware with the USB device connected to it).
I would try editing extras\google\usb_driver\android_winusb.inf in the Android SDK so that it recognizes your device.

The file should have a section like this that you can extend:

[Google.NTamd64]
; HTC Dream
%SingleAdbInterface%        = USB_Install, USB\VID_0BB4&amp;PID_0C01
%CompositeAdbInterface%     = USB_Install, USB\VID_0BB4&amp;PID_0C02&amp;MI_01
%SingleBootLoaderInterface% = USB_Install, USB\VID_0BB4&amp;PID_0FFF


If you go into the Windows Device Manager and view the properties for your device, you should see the ID you need.  For example, my Vibrant says USB\VID_04E8&amp;PID_681C under Device IDs and has 3 entries with that and &amp;MI_00, &amp;MI_02, and &amp;MI_03 appended under Bus Relations.  I would therefore add this to the .inf file:

; Samsung Vibrant
%SingleAdbInterface%        = USB_Install, USB\VID_04E8&amp;PID_681C
%CompositeAdbInterface%     = USB_Install, USB\VID_04E8&amp;PID_681C&amp;MI_00
%CompositeAdbInterface%     = USB_Install, USB\VID_04E8&amp;PID_681C&amp;MI_02
%CompositeAdbInterface%     = USB_Install, USB\VID_04E8&amp;PID_681C&amp;MI_03


You should also reboot into the bootloader, recovery mode, etc. and see if that provides more IDs.  I know my Vibrant installs new drivers the first time it's connected in each mode, so likely there are more entries needed.

Then just update the driver and select this .inf file.  It will probably give you an error about Driver Signature Verification. Depending on your version of Windows there are different ways to temporarily disable that; here is a good guide for Windows 8 and 10. Once it's disabled, install the .inf file and you should be good to go.

I think once you've done that then the USB Mass Storage drivers and so on will be auto-installed when you mount the device to the PC, but if not you could probably extend this process for that.