I think it's possible but not very useful. If I'm right, the way to do it is to have two separate HDDs, with an OS on each. The trouble is (or at least I think it is, I don't claim to be an expert) that you would need to open bios and choose which disk to boot from any time you wanted to change from one OS to the other.
I do exactly this all the time.
On my main PC, Win 8 and Win 7 on two different drives. Neither know anything about the other. On boot, enter the boot menu and choose which drive to boot from.
On a different laptop, Win7 and LinuxMint on different partitions on the same physical drive.EasyBCD
makes maintaining a boot menu easy.