[ubuntu] Ubuntu 12.04 LTS CD does not boot after Windows XP PRO SP3 installed

Was running Ubuntu 12.04 LTS on 32 bit Dell Dimension (older pc) without problems. The only OS on the machine. Needed to convert machine to a dual boot with Windows XP. So blew away the partitions and started over. Installed Windows XP with SP3 as the only OS but with plenty of unpartitioned space left for Ubuntu. Now Ubuntu CD won't boot. Always restarts Windows XP, which runs fine. All other CD's, i.e. GPARTED, Boot Repair, etc. will boot from the CD. Therefore, the boot sequence of CD first is working. Reimaged the .iso and tried it again but still no help.

Any ideas? Need to get this as a dual boot with both Windows and Ubuntu on the machine.

Thanks.