Whenever I entered the nether in the snapshot dating back to 13w25a my Minecraft would always crash and I would think nothing of it. Then after a point my Minecraft would crash after going through the portal and I would not be able to log back onto the server because the game would constantly crash.

I thought updating to Java 7 would do the trick and that helped it one time, otherwise sometimes I can log on and I see the nether portal but then I quickly leave the game as my Minecraft crashed again.

This is what appears in the launcher after every crash:
Game ended with bad state (exit code -805306369)
Deleting C:\Users\Matt\AppData\Roaming\.minecraft\versions\1.6\1.6-natives-40389058963801
Couldn't delete C:\Users\Matt\AppData\Roaming\.minecraft\versions\1.6\1.6-natives-40389058963801 - scheduling for deletion upon exit