download the kernel source from this URL:

-- ftp://ftp.redhat.com/pub/redhat/linux/updates/enterprise/4ES/en/os/SRPMS/kernel-2.6.9-22.EL.src.rpm

rpm -ivh kernel-2.6.9-22.EL.src.rpm

cd /usr/src/redhat/SPECS

rpmbuild -bp --target $(arch) kernel-2.6.spec

cd /usr/src/redhat/BUILD/kernel-2.6.9/linux-2.6.9

make mrproper

make menuconfig

-- Follow the link device drivers-> character devices-> Serial drivers -> 

-- Make "8250/16550 and compatible serial support" as module (M instead of * must be seen on the square bracket)

-- Disable "Extended 8250/16550 serial driver options"

-- Save Configuration.

make modules

make modules_install

make install

reboot Redhat and during bootup, make sure it boots with the newly compiled kernel

compile ISI driver and use minicom to test each of the modem.