If you have 2 gallery xml files in the same directory then, by necessity, they will have to be called different names but this is not a problem, as long as the xmlDataPath variable points to the correct file for each gallery.
However, as miker has noted, there is no sign of a gallery.xml file (or viewer.swf or swfobject.js) in your root directory.
As there is no xmlDataPath specified in either gallery1.html or gallery2.html, then both galleries will be looking for a file called 'gallery.xml' in the current directory. (This is the default action.)
What you could do is call one xml file gallery1.xml and the other gallery2.xml. Upload them both into the root alongside gallery1.html and gallery2.html.
Then, in your gallery1.html file, put:
... and in gallery2.html, put:
For the gallery to function correctly (with the relative paths as they are in your html files presently) you'll need to upload viewer.swf and swfobject.js to the root so that they reside at:
Both galleries can share these files and, being that gallery1.html and gallery2.html are in the same folder, the relative links to these files from both html files will be the same.
SimpleViewer Support Team