While the Cisco PIX family of routers use x86 processors, the firmware isn't PC BIOS compatible.
It really is a proprietary product, designed only to run Cisco's PIX operating system and related software..
Now, I'm not saying it would be impossible to run BSD or Linux on such a device, but neither would run unmodified.
I found one project showing how someone modified QEMU to run the Cisco PIX operating system, you can find more information about it
here.. but it appears to be the reverse of what you want.
Good luck.. keep us informed.. you could always just use a beige box like the rest of us.
