In the past, I’ve used our local mirror of the CentOS yum repository to kickstart machines booted using PXE; apparently, this no longer works with CentOS 5.1, although it did with 5.0. If you attempt to do so, after the initial PXE boot, you get the following message:
The CentOS installation tree in that directory does not seem to match your boot media.
The solution? Download the 5.1 DVD iso image, copy its contents to your disk and re-run the “pxeos” command to use that as your installation tree. I’m not sure if this was an oversight or a conscious change on the part of the CentOS project (or if the yum repository method was never supported in the first place), but it stumped me for a little while, so I thought I’d post it here.