Drivers are a pain, hope this helps (from memory)
In the CD image folder (not the actual image folder you select during the image download):
create $OEM$/Drivers/NIC - from here you can be as specific as you want such as:
$OEM$/Drivers/NIC/IntelPro1000VM
$OEM/Drivers/NIC/Vendormodelnumber...
I believe Microsoft recommends $OEM$\Drivers\$1\ or something similiar. Either way will work so you have something like this:
Image folder name\$OEM$\...... (not "in" the I386 folder)
Copy the 3 files you need, I believe it's: .inf .cat and .sys- NOTE: you may have to try different files, it may not work the 1st time. Check the manufacturer website for model and RIS specific drivers. Sometimes you have to use 2000 drivers for an XP image. It is trial and error at this point.
Also you have to copy the files into the I386 folder of the CD image. Sometimes a file with the same name will already exist. Try them both (don't forget the $OEM$ folder and the file that is there may conflict) copy or rename before you delete or overwrite.
One last thing that will not have to be tested is the path. In your answer file, you must put the path. I'm almost positive we do this in both images (the CD image and all of the images you select from the RIS menu on download).
Good luck!