CTRL+ALT+F1 takes you to runlevel 3, which is command line. You may need to login again.

CTRL+ALT+BACKSPACE kills the GUI, but X restarts instantly (usually) in this case.

Edit: Sorry, didn't notice you said 'boot' into text mode.

You may want to open YaST and then 'System' in the left menu. Go to 'System Services' (Runlevel) in the right menu, and choose 'Expert' tab. I believe you can set the runlevel, after booting, to whatever you like. But I've never tried it. Since it's set to 5, this is good bet that you can change it here.