You must change to Portuguese Brazilian ANBT 2.

Hi PhilG!

I'm Brazilian and I work with an american keybord! Every time I use shortcuts.

You have to change the language of your keyboard. Change "United States" to "United States - International".

After that, open your notepad and try to write "ç" ( , + c) 

It should work! If it does not, message me =D

This one should help:
http://symbolcodes.tlt.psu.edu/bylanguage/portuguese.html#winalt
(scroll down to "Windows Alt Codes")
You`ll have to use the numpad for typing the numbers.

Good luck!

I am using windows 7 so I'm not really sure about windows XP, but I think it is basically the same. Just go to your Control Panel, in the "Clock, Language and Region" section, then you can alter your keyboard. You just have to install the Portuguese keyboard (actually, I believe you just have to add it to the list of keyboards you have or something). The good thing is that you can type English, Portuguese, Spanish, French and several other languages with the Portuguese keyboard. After doing that, you just have to change the keyboard you are using in the language tool bar. Here you have a printscreen: 

http://25.media.tumblr.com/ff6049dbf1888262c0dfee370734cd29/tumblr_mgbos2xgM11qg59u1o1_1280.png

You will need to memorize the keyboard to find the accents. 
An image of the Portuguese keyboard to help you:

http://t1.gstatic.com/images?q=tbn:ANd9GcQHFIeR_gOdjCoB_D6XTEaAofrSiMJFaCChw8mZjaKd7p24w_b76CkuCYVOKw