can i start the *DM (e.g. kdm) on tty7, but not present on the screen?
For example, i want to stay at tty1 while the login manager is waiting on tty7 on boot.
You need to tell the X server not to change the vt (virtual terminal). There's an option for this: -novtswitch. With kdm, it should be added to the ServerArgsLocal line in kdmrc.
The bad news is that this option seems not to work in X.org (it prevents X from switching the vt when it exits!). Google turns up many reports, but no solution.
Depending on your needs, you may be able to get away with letting X change the vt, and then changing it back with the chvt command after a few seconds.