Boot code manipulation

[Michael Shergold]

I have a box with one of the motherboards and BIOS's (old 486 mini tower PC) where the SmartBootManager apparently cannot detect the CD drive though the drive works perfectly from MS DOS and WINDOWS. The machine is also connected to a LAN and hence the INTERNET or other local processor(one with Ubuntu running).
I can't be the only person like this who therefore cannot boot the UBUNTU CD.
Has anyone managed a hardware/software tweek to allow loading UBUNTU from either the CD or ethernet.  Or produced a floppy that forces a boot from CD0.  Or is there a H/W tweek like making the CD temporarily the primary IDE device that would work?
I can load the RIP floppy to get GRUB loaded but I suspect I need 38x machine code tools to poke the bytes required to change the load device to CD.

Any suggestions please 
Michael