Sure, so you can simulate that by creating your own name/value pair class.
Now, keeping in mind webservices aren't about classes and objects, but the
class you create in the .NET code is used to express what XML representation
you want on the wire. So something like this would work:

class Container
{
public string Key;
public string Value;
}

[WebMethod]
void TakeThis(Container[] items)
{

}

So the Container class can contain whatever primitives you want (int, double,
DateTime, etc). You can create class/object models in code like the above,
so Container can hold references to other objects, but again, keep in mind
that it's all being mapped onto XML Schema. So as long as you build simple
classes to hold your XML data and don't add method to these classes, you
should be able to represent the types of XML data structures you want to
accept in your web service.

-Brock
DevelopMentor
http://staff.develop.com/ballen