Is it possible to have an entire hard drive visible only to one user account on Windows XP Pro?

Yes and no; such practice is not recommended. How is that user going to start Windows? Unless it is second hard drive. Don't deny others, just take them out of allowed list. You must be careful - system must have full access to it!

Of course, all you have to do is to have partitions on drive formatted in NTFS and then set up security.

It's a 2nd hard drive that's used solely as storage space: there are no system files on it.

Okay, I figured out how to deny access to this hard drive from certain user accounts, but how do I make the drive invisible to these other user accounts?