As soon as I press play on snapshots 13w19a and 13w21a. it will give a popup window saying Minecraft has closed unexpectedly (see screenshot provided).

In the console it gives the error
Client> 2013-05-24 15:26:10 [CLIENT] [INFO] (Session ID is 3048378305292152701)
Client> Invalid memory access of location 0x0 rip=0x0
Client>
Game ended with bad state (exit code 139)

Version: J2SE Runtime 5 Update 30
Operating System: Mac OS X 10.5.8 Java Architecture: 32-bit