/sbin hasn't been in PATH in RH for a long time. It goes way back. For anything in /sbin you have to use the full path, /sbin/[command]. It's in path for just about every other distro I can think of. It's just an RH quirk.
For bridge configuration:
http://www.tldp.org/HOWTO/Bridge+Firewall.html
http://www.sjdjweis.com/linux/bridging/