Hmmm, I guess you might misunderstood the XS concept. The AI files (and alspo triggers and RMS) are written in C or something very similar to it. I've also seen everything is combined with XML, actually the whole game is written in XML (XML being the "data-marker").
C is quite easy to learn, I suggest you just start either with C right away or of you are a website programmer you could also learn php which is very similar to C. Basicly it's just a language like Pascal, with if, else, while, variables, functions, etc.
XML is something different though. If you have a look at the source code of AoM you can see a lot of stuff looks just like html (with the tags and such). Of course the elements aren't existing ones, and this is what makes XML so great. With XML you make your own tags, and you use these tags to give info on certain data.
Example:
<
myth_unit>Cyclops</myth_unit>
So, the tags say that a Cyclops is a myth unit. Anyway, thanks to this, and also other stuff EO found out about AoM will be very modable, or even total conversions won't be that hard to make.
Anyway, while waiting for AoM you could maybe start learning some XML: http://www.w3schools.com