he mean you will have to split your hard drive into a bootable storage for windows 7/vista/xp so you can run and play gunz there, windows 8 now home screen likes to programs in the background and gunz has not been allocated with windows 8 as of yet, so you will find most unallocated games not to work with windows 8, you will just have to downgrade / wait for a patch( not recommended it could take years.)
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thank you
~Resonate