illegal char in XML

When parsing an XML file, our program falls over when it encounters the umlaht(?) character. This is a foreign char which looks like 2 dots above u's anbd o's. Does anybody know of any workaroundsor patches, or is this a limitation of XML?
Any help would be appreciated.

I believe you will have to write a DTD or Schema to allow special characters for a certain node.

Thanks for the reply. Unfortunately I'm new to XML and am looking after an existing system so I wouldn't know how to go about making the modifications. Luckily our data supllier has said they'll remove them from the input files. I'll have to wait until I've gone on the course before I tackle it using your method. Thanks anyway:D

RSINGH, could u please give me a good example of what XML is good for ? i have started learning it and i dont know why, i only know the basics (xml w/ css styling) and want to continue but only with a reason. please ?