You should have and be running the new kernel you built (something like kernel-2.6.9-42.0.3.EL-prep), please check and make sure; name -a
If not then boot to this new kernel, you have to select this yourself when the grub splash screen is displayed.
The firewire modules should be in /lib/modules/2.6.9-42.0.3.EL-prep location, check.
You might want to try one of the CentOS plus kernels also, for example;
$ rpm -qlip kernel-2.6.9-42.0.3.plus.c4.i686.rpm | grep 1394
/lib/modules/2.6.9-42.0.3.plus.c4/kernel/drivers/ieee1394
/lib/modules/2.6.9-42.0.3.plus.c4/kernel/drivers/ieee1394/amdtp.ko
/lib/modules/2.6.9-42.0.3.plus.c4/kernel/drivers/ieee1394/cmp.ko
/lib/modules/2.6.9-42.0.3.plus.c4/kernel/drivers/ieee1394/dv1394.ko
/lib/modules/2.6.9-42.0.3.plus.c4/kernel/drivers/ieee1394/eth1394.ko
/lib/modules/2.6.9-42.0.3.plus.c4/kernel/drivers/ieee1394/ieee1394.ko
/lib/modules/2.6.9-42.0.3.plus.c4/kernel/drivers/ieee1394/ohci1394.ko
/lib/modules/2.6.9-42.0.3.plus.c4/kernel/drivers/ieee1394/pcilynx.ko
/lib/modules/2.6.9-42.0.3.plus.c4/kernel/drivers/ieee1394/raw1394.ko
/lib/modules/2.6.9-42.0.3.plus.c4/kernel/drivers/ieee1394/sbp2.ko
/lib/modules/2.6.9-42.0.3.plus.c4/kernel/drivers/ieee1394/video1394.ko
The kernels can be found here;
http://isoredirect.centos.org/centos/4.4/centosplus/
.