Thanks, I'd actually worked that out myself. I'd still like to know where to find the schema though so I can have any XML I create validated. It might also help when I eventually get round to installing Visual Studio too,.
I think the problem with getting the schema is to do with using kchmviewer to view the chm documentation (IE7 will not display it at all) --- I found the documentation here
http://mpscripts.net/docs/ref-interface-schema.php and downloaded the schema.