When I try to boot a DFI LanParty-UT CFX3200 from a Windows 8.1 Preview DVD without having Windows 8 installed I get a
DISK BOOT FAILURE, INSERT SYSTEM DISK AND PRESS ENTER message.
Do I need Windows 8 to install Windows 8.1 Preview?
No, you do not.
I'm unaware of any upgrade options for the Windows 8.1 Preview, but even if there are upgrade options you should be able to boot from the disk (in previous upgrades this was the case).
There's likely a problem the image you've downloaded, with the DVD you've burned, or your boot options. Ensure you've selected your DVD drive (I'm assuming you burned a DVD) as the primary boot option, or selected it as the temporary boot options. Failing that, burn another DVD. If you still can't get it to work, download the ISO again.
Might not hurt to pick through the manual on your motherboard either.