Xml WebService return type?

Hi,

I must build an xml webservice (in vb.net) that will return xml to the middle tier.
I'm not clear what will be the best way to declare the return type, because this web service need to be called from both vb6 components, and vb.net assemblies. So I understand that I can not use ado.net dataset. It seems that the xml format will work, but in what format :
<web service>Public Function MyFunc() as ....?

And I have one second question: How do I send an dataset as xml from the webservice. (I'm not sure:I need to define a stream, load the dataset into the stream, save it to a string (stream.savexml ?) and send the string as the return parameter).

A small ex will be great.

Thank you,

Sorin