Normally, my albums are sorted with the newest image being first; however, I'd like to sort some album alphabetically by providing a link to do a one time sort. One such album is this one: http://gallery.mysstie.com/landmark/outfits/

Thanks,
Mark

You can set the sorting via the object model using the album class methods setSortType() and setSortdirection(). You could naturally set that either via POST or via an additional GET query on the url.

Note that setting that will be permanent. If it should be only for that user you probably need to set cookies or something.

I couldn't figure out what file to modify so I just made a separate listing here for now: http://www.mysstie.com/landmark-outfits.php

Which file should I check the Get variables and adjust how the album is displayed?

You could do that right on the album.php page or via a plugin.

yoursite.com/youralbum/?sortorder=xxx

Then you would have to change the order via the object methods before you output the images of the album. As said those would be permanent set for the album. If you wish individual order per visitor or even by album it gets a bit more complicated.