>I want to go one step further and actually *set* the serial number through the API. Have you ever seen that done? A software problem just jumped into my lap where the app registration was linked to the HD serial number (I hate that) and now that the HD contents were moved to a newer larger drive, the app won't run. :( I know the old serial number, so if I can just change it on this drive I'd be set...

SetVolumeLabel() is as close as you can come. The API provides no functionality to directly set the serial number. In order to do so, you'd have to access a couple of ROM BIOS interrupt calls. Specifically, Int 21h Function 440Dh Minor Code 46h and 66h for FAT32. In order to do so, I think you'd have to write a virtual device driver in C.