Well, figure out what it's supposed to do and then ask a specific question about that. I'm not really clear on what it's doing. It seems to be getting the serial number from the first drive with a letter between C: and Z:, modifying that number, and then using it to seed a random number generator. Then it does some bit-shifting and starts to pull some random numbers.

The question is: what are you trying to do with this code? Give us a little information about the environment you're running this in and what you're trying to accomplish. Win32::DriveInfo seems like it will do most of what you want, but it's still not clear what the purpose of all this is.