It's not possible. Gamers have been dealing with this topic for some time.
Furthermore, moving windows by using Alt+click isn't a feature of only Compiz. Metacity, the default window manager in GNOME (and hence the fallback when Compiz is disabled), does just the same thing.
Looking back to your original reason for wanting to do this, one workaround would be to use the "Windows" key instead of Alt:
- Change the setting at System -> Preferences -> Windows -> Movement Key
You can also choose to disable the feature entirely:
- If you're using Compiz, open CompizConfig Setting Manager and disable the "Initiate Window Move" binding for the "Move Window plugin".
- If you're using Metacity, run
gconf-editor and set
/apps/metacity/general/mouse_button_modifier to be blank.
It seems to me, though, that the most appropriate solution would be to change Inkscape's behavior:
- The Inkscape FAQ describes the modifications you will have to make to one of Inkscape's configuration files.