The default keyboard setup of Apple's X11.app for Mac OS X doesn't support Alt- shortcuts in KDE apps (at least not when KDE's installed via current fink, e.g. by sudo /sw/bin/fink install kdebase). This makes konsole just about unusable, as konsole translates Alt events into Meta keypresses on the underlying terminal, and discards true Meta events. To fix this, assign the keycodes as follows in your ~/.Xmodmap:
keycode 66 = Alt_L keycode 69 = Alt_R
Then, ensure that your X11 "Preferences..." are as follows (dialogue box is from Leopard):
Finally, restart X11.
For completeness, here's the keyboard layout kcontrol module (you shouldn't have to do anything here, as these are the default settings):
Credit to this macosxhints.com post, which took an astonishing amount of searching to sift from the vast oceans of trash and non-working solutions that you get when you search for X11 issues for Mac. I post this in the hope that it will serve as more efficient Google-food.
(Background: I recently killed the hard drive on my ~2.5-year-old work MacBook, and so I've been reconstructing my work environment on the shiny new MacBook they requisitioned for me. Running emacs in a screen session on a remote Linux box is one of my most common activities, so having konsole with no Alt/Meta makes Mac usage just about unbearable. I could not for the life of me remember the magical incantation I did to fix Alt last time, so I literally spent about half a workday intermittently typing random permutations of "kde", "fink", "alt", "meta", "konsole", and "leopard" into my web search box. Blech.)