No Encryption for Windows Xp

Having recently set up my new 2TB WD MyBook, I tried to access it from my work pc which runs Windows XP. Upon connection I got a message stating something llong the lines of “encryption does not work unless I upgrade to at least Vista”. Unfortunately I stupidly checked the message so that it does not show any more, so could someone please explain what the security implications are?

Many thnaks

How are setting up the encryption?

Try this

Just to be clear, are you using the option to use password protection to lock the my book.