securing IE 5.5

i have a citrix server where i have published IE 5.5. I am having a problem of users getting access to the local server drive (C:)..they type in C: in the title bar and get right into the drives. How do I prevent this? The local policy of “prevent users from accessing drives” cannot be used because of other apps that require access via the application..behind the scenes of the user. anyone ever come across this?

Thanks!

Steve