Here’s an e-mail from Jamey Kirby, posted to NTDEV, on how to keep Explorer from showning a drive. I love it!
Use numbers for the drive letters. You can access the drive via 3:\yadayadayada\yadayadayada. You can even park a CMD prompt on it, but explorer and associated APIS will not enumerate them. Jamey
Jamey gets a Gold Star(TM) for pointing this out.