Are you using Linux, BSD, Mac OS or Windows with Cygwin/MinGW?
If Linux, you may not have mkisofs installed, but you should definitely have losetup and it should definitely accept the -f argument. The 'f' is for "free",
should return the first free loop device. You should be able to find a package containing mkisofs with your package manager's search function, e.g.
apt-cache search mkisofs
. If not, you can download it here: http://freecode.com/projects/mkisofs
If you're using BSD or Mac OS, then there is a different command than losetup (vnconfig), but mkisofs should be the same.
If Cygwin/MinGW, you'll need to install both mkisofs and losetup, but I don't know if they're even available. I imagine they would be, though.