I am in the process of migrating my desktop system from 32-bit CentOS 4.8 to 64-bit CentOS 5.4. One of the things I want to be able to do is boot my IBM Thinkpad X25 laptop via its PXEBoot ROM over the LAN (it has a hard disk and boot locally just fine, I just want a way to boot it for rescue and/or new O/S installs). On my 32-bit CentOS 4.8 this works just fine. It also works on another machine, running 32-bit CentOS 5.4. On my desktop system running the 64-bit version of CentOS 5.4 it does not. The DHCP part works fine, but I get a 'TFTP ARP TIMEOUT' message. The various config files are all the same (or consistent). I cannot figure out what is wrong. If I let the laptop boot up normally, it is happy to use tftp to fetch pxelinux.0 from the 64-bit CentOS 5.4 system. It just won't fetch it from the boot ROM. What am I missing here?