Tripwire is technically no longer in development, although it is still a fantastic tool that we use on all our servers. It is not available in an RPM format that is compatible w/ RHEL.
However, a group of developer(s) has started the tripwire-portable project based on the tripwire source code. It seeks to improve upon tripwire and make it more compatable across platforms. The functionality of tripwire-portable is exactly the same across all systems, and it can compile cleanly on most major *nix distros. We are using tripwire-portable on all of our FC3 boxes w/out any problems. Also, the default config/policy files that come w/ tripwire-portable are much simpler and cleaner and can be adapted much more quickly to your enviroment than the default files that come w/ tripwire.
Tripwire-portable home page:
http://www.frenchfries.net/paul/tripwire/
Installation instructions:
http://www.linuxfromscratch.org/blfs.../tripwire.html