"2.4.0 will not be released for SnowLeopard. 2.4.1 will be the first release that can be installed on SnowLeopard. There will be separate Leopard and SnowLeopard packages for 2.4.1 and later."
How did you install X11 on snow leopard? My old version of X11 has problems with keyboard mapping after logging on to my Ubuntu desktop via X11 on the Mac.