I have to correct myself once more:
It wasn't in /boot/grub/grub1st or something, where to set init 3.
It was the file /etc/inittab
There it says something like
You can edit this to
then you should be able to boot to console, where you can look for another windowmanager.
By the way: I just tried enlightenment with an aqua-theme.
That somehow killed my X-server completely. It wouldn't start kde nor windowmaker. I had to reinstall.
I hope you don't have to.