I customised runlevel 4 few days ago, getting rid of all unnecessary services and putting it on grub screen as a boot alternative.
Seems to work allright although intermittent problem with backspace.
On Debian went to /etc/rc4.d ?? It is full of symbolic links to the services, e.g. ppp, cron, atd, etc. It is called from the first file that init looks at: /etc/inittab ?? Made a subdirectory in rc4.d and put the symbolic links I didn't want in it.
Only problem was only had one blackscreen, F1 - not alt-(F1-F6). However edited inittab to put right.
Should have said: put
init init=4 or something, at the end of the line with 'kernel' in it, in grub's menu.lst configuration file. This to boot into runlevel 4.