These two keys use a 32-bit bitmask to define local and network drive access for each logical drive in the computer. The lower 26 bits of the 32-bit word correspond to drive letters A through Z. Drives are visible when set to 0 and hidden when set to 1.
If your not happy working in Hex, add these decimal numbers to hide the drive(s):
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: 67108863
For example to hide drive A and drive D, you would add 1 (A) + 8 (D) which means the value should be set to "9".
To disable all the drives set the value to "67108863".