Yep, the display manager will do that.
If it's a "once off" thing, just press Ctr-Alt-F1, and switch to the first virtual console (eg, cli - there's 6 of them, plus the X console...). Then login, and type "telinit 3" to drop to run-level 3 (multi-user text-only mode). Then do your stuff, and type "telinit 5" to bring it back up to run-level 5 (multi-user X mode).
There's lots of ways of getting there, including editing /etc/inittab to set the default run-level, and passing "linux single" as a lilo kernel parameter to boot to single-user mode (text-only safe mode, I guess).
<i>Knock Knock, Neo</i>