Thanks for the info. After perusing these sites, I am thinking that the Ironkey concept is what I am looking for, more than either of the others.
The Mac is mine -- I have full control. The XP machine is part of a network -- it is password secured, I don't have administrator rights, I don't even have access to the hard drive (all data is stored on servers; I cannot install any programs or apps). However, instead of using the server as storage, I save data on my USB flash drive and access this data on both computers.
So, I need password protection for the USB data that is independent of OSs. Are there USB drives other than Ironkey with this feature?
I recently bought and received an Ironkey USB flash drive. It works as advertised and is perfect for my needs -- OS X and Windows cross-platform, and password security. Easy to set up, easy to use. I would recommend this to anyone who has confidential information (about themselves or others) on a USB flash drive. If lost or stolen, the contents cannot be accessed. Indeed, the contents are destroyed after a certain number of consecutive false password attempts.