Houcos, you asked about installing Unix and Linux OS in one machine.. actually Linux came from Unix, its one of the variant of Unix. You can install it. But make sure your H/Ware requirements are good enough.. .
Yes. If you browse http://www.freebsd.org and http://www.linuxdocs.org you'll find TONS of information on most of the things you'd EVER want to do. Look for a dual-boot HOW-TO on linuxdocs...