Fedora Extras is for FC3 and newer:
http://download.fedora.redhat.com/pub/fedora/linux/extras/3/SRPMS/
I repackaged openal from FC3 on my FC2 system. I can't imagine anything in the SRPM that would be incompatible. I wouldn't upgrade a core component like a kernel or glibc that way, but an add-on like openal should be ok. (I looked at the resulting file list and install scripts to make sure it wouldn't do something evil.) The more critical the component is, the more closely I inspect the spec file and patches before proceeding.
(I figure I'll upgrade the box to FC4 a month after it's stable, allowing time for the "surprises" to die down a bit.)
