I'm trying to install Wine on Red Hat Enterprise Linux using Yum, but it's not in the RHEL repository. How can I install RHEL via Yum? I'm pretty sure there may be other repositories out there somewhere which have a RHEL compatible binary (maybe CentOS), but I can't find them.
Have a look into adding the EPEL repository to your RHEL build. EPEL is Fedora packages built against RHEL http://fedoraproject.org/wiki/EPEL I have not used this repo to install wine but do currently have it installed in my Scientific Linux 6 RHEL clone.
If you are not familiar with install 3rd party repositories then you may want to have a peek at the centos documentation here: http://wiki.centos.org/AdditionalResources/Repositories
I also use Atrpms but that is probably overkill for your requirements.