Compose Special Characters
The Compose Special Characters extension for OpenOffice lets you type two or three characters and then run a macro to convert them into a single accented or special character. Writer and Calc are currently supported.
You can also use a dialog to insert any supported character. The dialog lists all supported characters and the character combinations you use to compose them. The characters are categorised in the dialog for easier reference.
Once you know the character combination you need for any particular character you don't need to use the dialog if you assign the ComposeSpecialChar to a keyboard shortcut. You can then type the character combination and press your shortcut key to get your composed character as you type.
To open the dialog choose Compose Character... on the Insert menu (Insert > Compose Character...).
You can assign the ComposeSpecialChar macro to the keyboard shortcut of your choice via a button on the dialog, or you can manually assign it to whatever key combo you choose via Tools > Customise... > Keyboard.
To assign a keyboard shortcut:(You can use that same procedure to unassign the shortcut using the "Clear shortcut" button, for instance if you make a mistake.)
HOW TO USE
After installing the extension you'll need to close OpenOffice then re-open it to see the new Compose Characters... menu item on the Insert menu.
See "To assign a keyboard shortcut..." above.
Type the two composing characters and press your shortcut key to get your composed character.
Type a "flag" character plus the two composing characters, then your shortcut key. A flag character is required in Calc because there doesn't seem to be any way for a program to identify where the insertion point is in an OpenOffice spreadsheet cell. Since you might want to insert a special character anywhere in a cell, not just as the last character, the flag character is necessary.
You can choose your own flag character in the Compose Special Character dialog. Remember, whatever flag character you choose, it should be one that you're not going to use in a formula or a value.
Update:
To update an OpenOffice extension, choose Tools > Extension Manager... > Updates... in your OpenOffice program, like Writer or Calc.