guess r3sistance is right, by default there is no /etc/inittab file in ubutnu 10.04 ( haven't checked with the previous version) the run level is set by the file /etc/init/rc-sysinit.conf. in which the default runlevel is set to 2, so the GUI runlevel in ubuntu is actually 2.
We can modify this by setting the required level in the line
Or by passing the runlevel as an argument during the boot i.e,
press esc while grub is loading.
press "e" when the cursor is on the version of linux you are booting
move to the line that starts with kernel
add 3 to the end of this line
or by running the command
this might be useful