Similar to the Easy German Umlauts on an US keyboard for X11, I have created a keyboard mapping that can be used on Windows XP to enter German Umlauts on an US keyboard.

The keyboard layout was created with the official Microsoft Keyboard Layout Creator 1.4. If you just want to use the layout, install the corresponding .msi file from the .zip archive (I really do not know why Windows needs a different file for the different platforms). If you want to modify the keyboard layout yourself, you can download the Keyboard Layout Creator from Microsoft and then use the .klc file.

The following key-combinations have been defined:

AltGr-a               ä
AltGr-A               Ä
AltGr-o               ö
AltGr-O               Ö
AltGr-u               ü
AltGr-U               Ü
AltGr-s               ß

AltGr-'               Dead Version of '
AltGr-^               Dead Version of ^
AltGr-`               Dead Version of `