This is taken from "The Sarah Lane Files" on "Attack of the Show" (fomerly "The Screen Savers")
This is a" how to:" guide for hiding your hard drives so they won't show up in "Windows Explorer". thanks to the lovely and talented Sarah Lane

originally posted here: G4

Sarah's Windows Tweak: Hide Your Drives
written by Sarah Lane on Thursday, May 27, 2004
Make your private data invisible to snoops by hiding your hard drives.
Ever wish you could make one of your computer's drives invisible to anyone snooping around on your system? Well, happy days are here my friend! Follow my simple directions and you'll be a magician in no time. Whether you have sensitive docs, pictures, or any other private data, this is one of the easiest ways to keep them safe. Keep in mind that you'll still be able to access your hidden drives; you just won't see that they exist in Windows Explorer or the My Computer folder. Back it up, back it up, back it up All together now: "I must back up the Registry before tinkering with it... I must back up the Registry before tinkering with it... I must back up the Registry before tinkering with it." Now that you've talked the talk, it's time to walk the walk. Learn how to back up the Registry and do it before proceeding. You'll thank yourself for saving your existing settings if anything goes wrong, so be safe rather than sorry.

Let's hide those drives

1. Open Regedit.

2. Navigate to this string: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer

3. In the Explorer key folder, create a new DWORD value by right-clicking Explorer, then choosing New DWORD value. Name the value "NoDrives" (without the quotes).

This value defines local and network drive visibility for each logical drive on the computer. All drives will be visible as long as this value's data is set to 0.

4. Following the table below, enter the decimal number corresponding to the drive(s) you want to hide as NoDrives value data. When you right-click on NoDrives and choose Modify, make sure you select Decimal base, not Hexadecimal.

Drive Number to hide

A: 1

B: 2

C: 4

D: 8

E: 16

F: 32

G: 64

H: 128

I: 256

J: 512

K: 1024

L: 2048

M: 4096

N: 8192

O: 16384

P: 32768

Q: 65536

R: 131072

S: 262144

T: 524288

U: 1048576

V: 2097152

W: 4194304

X: 8388608

Y: 16777216

Z: 33554432

All drives= 67108863. If you want to hide more than one drive, you simply add the drive amounts together for a combined total. For example, to hide the D:/ and T:/ drives, add the decimal value for the D:/ drive to the decimal value to the T:/ drive. 8 (D) + 524288 (T) = 524296

To disable all of your visible drives, set the value to 67108863. You must reboot your PC to see your changes.