by Howard Miller.
A quick Google implies that the xml-rpc extension is enabled by default in the windows version.
With my "this is nothing to do with Moodle" hat on, you might get a better/quicker response over in the "apachefriends" forums. I don't want to appear unhelpful, but I'm unsure how much Xampp knowledge you will find over here.
On the other hand... why didn't you just install Moodle from the Windows installer available here on moodle.org. I would assume that it has all those issues sorted out (and it's Xampp based)?