Tronko,
you will have to use the html safe equivalent to these characters. For example in XML you cannot use " " you have to use " " which is exactly the same but XML safe. It also goes for all the characters that you need to use.
Eg: The trademark sign (TM) can be used properly by using ™ and é has to be represented by é
You will have to find the equivalent for your character by writing a quick html file that have all the different numbers in it and the character they represent
eg:
151=ç<br>
152=è<br>
153=é<br>
154=ê<br>
155=ë<br>
156=ì<br>
157=í<br>
158=î<br>
159=ï<br>
150=æ<br>
Theres are quite a lot of them, I have got one that goes from 1 to 999, I don't know if there are any beyond that.