lonmae,
If the motherboard bios can detect the full 30gig then drive overlay such as Ez-Bios is not required. If it can't then you should see if there is a bios upgrade available and re-flash if possible before using drive overlay.
DOS has a 2gig drive limitation as well, so that defeats having one 30gig partition also though you could create a minimum of 15 partitions on a 30gig drive using DOS Fdisk with out drive overlay such as EZ.
Turning off drive overlay usually requires running the overlay software and setting it to "Not Controlled by Ez-Bios" (or something like that).
You could then boot with a DOS disk, run Fdisk and then remove the Non-Dos Partition. Its been a long time since I have used any overlay but not long enough to forget the headaches of it.