Thanks Petru, that was very helpful. I think the time saved using the XML-RPC solution would probably off-set the cost of the extra machine. I've been researching some XML RPC solutions for ACS, there seems to be quite a choice. Hopefully, there's one available that will work with Classic ACS 3.4.
BTW, are there other alternatives as good as XML? As I'm writing the wrapper for the dll, I have total control of how the data comes back, it can be in any format I choose. Or is the main advantage with using XML to do with the amount of tools available?