Having spent all morning solving this problem, I thought I'd share the solution in case it helps someone else out there...

Problem:
Inspiron 530 and 545 PCs won't boot Ubuntu 13.04 live DVD. Boot error message shows. DVD works fine on other PCs

Attempted Solution:
Use USB image. USB stick works on other PCs, not on the Dells

Actual Solution:
1) Burn plop boatloader onto a CD http://www.plop.at/en/bootmanager/index.html
2) Make USB image of 13.04
3) Run plop from CD
4) Choose USB and boot into 13.04

Hope this helps!