Unlikely, normally they don't touch the hard disk (unless something goes
wrong, or it has a virus, or both).
Safest thing: make a (disk)image of the disk and play it in some emulator.

DON'T DO IT! It will infect the internets with a booter virus which will cause all computers to boot booter games. OMGWTFBBQ!

It doesn't "take over" the OS. The system simply boots from that floppy and doesn't start the one on the hard drive. If you remove the floppy and reset the computer, the installed OS (Windows, probably) will boot. The program on the floppy doesn't need an OS or at least has all the functionality it needs coded into it.

But if it's an infected floppy it could corrupt the MBR, boot sector or the whole hard disk data.

I think what we really need to be asking is why he's putting a floppy into a "new" computer. Is this his 2.6ghz machine or his 1.3ghz downclocked to 500mhz machine? heh.

/Still sticks floppies into new computers.
//Loves teh floppy.

I thought the 500 mhz computer was 1.3 ghz. The 500 mhz computer has a floppy drive and the 2.66 computer has no floppy drive.