I remember I could boot from terminal and then log into gnome as I pleased with Ubuntu. And since ubuntu derives from Debian I figured I would be able to do the same. Don't knwo shich file to edit though...
/Richard
Check your /etc/rcX.d directories for the startup file which begins with a capitol S - disable it by either moving it to a different name (it will start if left as Sxxxxx - so move it to sxxxxx).
Or just change the /etc/inittab to not enter 'X11' mode.
I don't know what to modify to not start GDM. First I tried RTM's suggestion but my computer got into 'read-only' mode and I had to re-install the whole system. I realised I didn't do as you said (I misunderstood you) but still I'll try the4 simpler way...