I have a friend who at one point was booting Win98, Win2000, BeOS, Mandrake, Caldera, RedHat, and a couple other operating systems on the same machine. So yes, it's quite possible
But as digiot says, it may be hard to mix and match partitions with them... i.e., it's tricky to let two of them share the same /usr partition (though you may be able to share /home without much trouble).