XML writing

I have used data from a XML document before that I have created from scratch.
Now I need to create a XML file on the fly from a dynamic php page. I have
searched numerous places on how-to accomplish this and have not found anything
that actual worked. Does anyone know of a tutorial I could take that would
create a XML file based on parameters I set.

Thanks
Jim

Thanks David, but this example is not clear to me. I would rather see an
example of getting data from a form and then writing it to an XML file that has
not been created. Still trying to work through that example.