Well, it's not password protection but you can "hide" drive D see:
http://news.softpedi...-privacy-44023.shtmlThe drive will still be accessible merely by typing D:\ in Explorer's address bar, but most folks if they don't see the drive listed in My Computer probably wouldn't think of that. You could also probably go into Drive Management and change the letter to something like "Y" to be a little trickier. Someone might look at the size of drive C and think 'there has to be more...' but then, you're getting beyond the more casual snoop. Obviously, don't have any shortcuts available that connect to anything on the hidden drive and I'm ASSuming this technique hides the drive from file open dialogs.
Security is always a tradeoff between convenience and the cost of getting p0wned. Encryption or at a minimum NTFS permissions are really what you need if the data is worth keeping private. If I had personal/company data I didn't want people to see, I wouldn't keep it on a system that is other folks have that much unsupervised access to. Unless you demo account is locked down, anyone could install a keylogger or other malware that might compromise your entire system, much less the password scheme.