Kernel RPM re-compile from source RPM 

Download the .src.rpm package from your local mirror.

(As of FC3, the default build no longer includes the 'kernel-source' package, sadly, so we need to get it manually)

Install it:

rpm -ivh kernel-2.6.12-1.1376_FC3.src.rpm

cd /usr/src/redhat/SOURCES

edit all .config files that apply (i686 for example), and
add the two lines below to the end of it.

CONFIG_LEGACY_PTYS=y
CONFIG_LEGACY_PTY_COUNT=256

cd /usr/src/redhat/SPECS

edit the spec file identify the custom build release (remove the 'rhbsys' line at the end):

%define release %(R="$Revision: 1.1 $"; RR="${R##: }"; echo ${RR%%?})_FC3_pty

rpmbuild -ba --target i686 kernel-2.6.spec

find the rpm in /root/src/redhat/RPMS/i686, and install using rpm -ivh

check your grub.conf to make sure it's the default boot kernel, reboot.

after reboot, check that the new kernel is running, and verify the existance of '/dev/ttyx0' (and other /dev/ttyx[]) devices.