Try out Tiny Core Linux. You can run it on almost anything. It is crazy fast and can boot entirely to RAM. It isn't as full featured as other OSs but it can

Try out Tiny Core Linux. You can run it on almost anything. It is crazy fast and can boot entirely to RAM. It isn't as full featured as other OSs but it can boot of pretty much anything including floppy disks. If you want something more full featured I would recommend Debian.