Best way I’ve ever found for Windows: US-International keyboard driver. It has been around since at least Windows 3.1 as a native part of the OS.

Works seamlessly with virtually every Windows application.

Provides simple and quick access to many accented and special characters. Mnemonic and unobtrusive. In fact, even though I work mostly in English, I leave the US-International driver enabled as my default.

To enable in XP:

Control Panel | Regional and Language Options | Languages tab | Details

Under “Installed Services”, add United States-International as one of the Keyboards.

(Set it as the default input language if you wish. Otherwise, switch between/among keyboards using an icon on your taskbar or a hotkey.)

Quick primer: my most frequent alternate language is French. I can access all French accents using three standard QWERTY keys which have now become “dead keys”–the apostrophe, the circumflex (Shift+6) and the “accent grave” (the key which also has the tilde, just to the left of number 1).

Press the dead key first, then the letter to which the accent will apply. Easy.

If you need the original value of these three keys, either:

1) type a letter which doesn’t take an accent after the dead key (for example, “t” doesn’t take an accent (at least, not in the languages I use!) so pressing apostrophe followed by a “t” gives simply ‘t) or

2) press the spacebar after pressing the dead key.

For other special characters (including the copyright, euro and degree symbols, fractions such as one half etc.) hold down the right Alt key while you press another key. Shift+rightAlt+key gives you a whole other selection.

Cheers,

Steven