Hello,
Where exactly isn´t windows xp recognizing the portuguese characters ? If
you don´t already have one you need a portuguese keyboard at least to know
where the portuguese characters are, and then you need to change your
language setting in Start-Control Panel-Regional and Language Options and
then add Portuguese as the default input language if you have more than one
you can actually change between them using the language bar that appears in
the taskbar or can be configured to appear even in the desktop itself.