I am not quite sure what the dimensions should be. I have seen a few posts that say 640 x 480 but one guy said he tried that and it looked stretched out. Oh and I noticed that, that search link doesn't work. Just go into a regular search and type in uxsplash.jpg and then make the search time like 180 days. And be sure to search all UnleashX forums and it should find some threads.
