Assumptions:
-You're using bash
-You need /sbin in the path of an ordinary user (ie not root - this would already be in root's path)
Naturally, you shouldn't add any of the sbin directories to global users' paths since the whole idea is that normal users won't accidentally run admin commands (even if they don't have the rights to do system-wide damage, they may screw up their own profile, get confused etc).
So, to add it only to your own non-root path, login as that user (or su -) and
vi ~/.bash_profile
after
PATH=$PATH:$HOME/bin
add
:/sbin:/usr/sbin
and then log out and back in again... you should be able to run sbin commands without the full path.
Hope that helps!
Ian