The above is the homepage of the FUSE code. FUSE is "Filesystem in USErspace" as mentioned by Elemecca above. It comes with many Linux distros, but exactly how many, I personally have no clue.
Google returned that link at the top of the first page I got from my search for "Linux FUSE".
As RHEL is a pay-for distribution, you should likely be able to get FUSE from your package repository by downloading and installing it, provided you:
A) do pay for the registration/support and for use of the package repositories, and
B) if it is available for RHEL4.
You cannot find official RHEL packages willy-nilly around the net. If you have a DVD or CD of your distro, chances are good that if FUSE were on it, it would already be installed into your system.
You might want to search the CentOS repositories for a FUSE RPM, and try to install it (which probably won't work, especially if the distro is not registered), or just switch to CentOS, which is free.