A great resource for learning about SELinux http://fedoraproject.org/wiki/SELinux
specific samba policy http://fedoraproject.org/wiki/SELinux/samba
For the most part, the information on the specific samba policy link above should take care of the things that most people need.
CIFS Broken in Samba 3.0.23a
The cifs support in the official 3.0.23a release is broken. If you mount a share using "mount -t cifs ..." you can see the files but attempts to access them result in a "Permission Denied" error.
The svn branch has been fixed so you can checkout the code and compile your own version or be patient and wait for the official 3.0.23b release. This is most likely to be a problem to Fedora Core 5 users where cifs has replaced smbfs which is no longer available as a mount option.