If you click on an equipped item with a charm quality, it should pop up a window that you can drag and drop charms into (up to your Enchant Weapon skill level).
If you already tried that and nothing seemed to happen, the charm pane may be opening off screen. Run the configuration program and increase the resolution, start the game, open a charm pane, move it into the center of the screen and close it. Quit, run the configuration program again and restore the original resolution; now when you re-start, they should open on screen.
If you are already playing at 1024x768, you can edit the config.div file to play at a higher resolution, such as 1280x1024.
