How are you trying to boot BT ?, according to the laptop compatibility list:
Dell Latitude D531
- Boots Live and installs on hard drive perfectly (also dual boot -XP, BT).
- Does not boot from CD ( stops at Floppy drive(s): fd0 is 1.44M )
Given the above: I would try disabling the floppy drive in the BIOS. Or attempt booting BT from a USB thumb drive. If you have the space, installing it on the hard drive should solve the problem. Buying a new laptop seems a bit extreme, without trouble shooting various methods first.