Working bootable USB boot stick, can bootable ISO be created from it?

[vr <debian-user@iotk.net>]

As the title says; can a bootable ISO be created easily somehow off a 
working bootable USB stick that is formatted FAT?

I tried dd if=/dev/sdb of=/tmp/myboot.iso

but probably that won't ever work since they're a different media 
structure.

Any suggestions?