I want to set Windows to search for new drivers in C:\DRVs or something like that, and not do the windows updates, etc. Just do a direct location search.

Is there a registry edit for that?

Yup

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion]

add the location to the DEVICEPATH key.

Google for 'SetDevicePath.exe' if you want an easy-to-use CLI tool.

This tool:

http://www.vernalex.com/tools/spdrvscn/

Also does a similar job of setting the DevicePath using a GUI, or commandline.

If I already have Winnit.sif and sysprep both pointing at C:\Drvrs, then I don't need to set the drivers for windows?

I think that the registry allows for unlimited characters to describe the driver path. It think if you use the sif file it will only allow 4096 characters.

It's not quite unlimited. It's great deal more than WINNT.SIF, but not unlimited. Something like 64kb is what I'm thinking.