Win XP + Win 2003 server + RedHat Linux 8.0 + My own custom Linux installation. I had FreeBSD but removed it because I couldn't get X running.
Ujjwal: Technically anything that runs by itself and helps other programs run is an OS. So a bootable floppy is definitely an OS unless it is just a bootloader.
it_waaznt_me: Check out this site *linuxcds.netfirms.com/. Thats where I bought my FreeBSD CDs. They deliver to most places in India and if you live in bangalore you can go there and collect them.
Deep: Linux is as stable and flexible as FreeBSD and Linux supports a lot more hardware than FreeBSD. And most open source software is developed for Linux. And also, as Linux uses GNU software, it has more "features" than FreeBSD. FreeBSD would make a good server though.