I just did a yum update and got the above kernel update installed. Upon install I found I couldn't build any of the kernel modules that I need (nvidia graphics, madwifi, etc). Looking in the lib modules area I found:
lrwxrwxrwx 1 root root 47 Jul 16 15:25 /lib/modules/2.6.12-1.1372_FC3/build -> ../../../usr/src/kernels/2.6.12-1.1372_FC3-i686
which I suppose explains the problem - I didn't make this link, so I assume the yum install made it this way, rather than install the normal kernel sources.