cant boot from large disk

[FreeBSD User]

Howdy Questions,

I am having problems with 4.8 Release booting from a large hard disk 
(80 - 160G) on an old (socket7) motherboard.

I have the same problem with linux. Making the root partition
smaller that 1000M, puting it on the first disk, etc etc  doesnt 
help in either case. I have also tried a few different bootloaders,
in all cases, the bootloader either failed to load, or failed to 
boot the OS.

With Linux (redhat7.x) I was able to build a bootable floppy on which
the location of the root partition was stored, and boot off that.
I could also interrupt the boot, enter different values, and boot
off of a different partition. Hardly ideal, but satisfactory.

I was kind of hoping to do the same thing with FreeBSD.
(which atm resides on a 160G HD with the root partition in a seperate
900M slice.)

Any hints ?

Cheers.