Ok, so what
do you see? What exactly is going on? Is it loading the first one but not swapping out properly? Is it not even bringing up the first one? If so, are you at least seeing a box appear where is
should be? Also, what browser (and version) are you using? It might make a difference (though I'm not sure yet). Anything you can think of to tell me about what you do and don't see happening might help. We'll figure this out if it's the last thing we do! :p
EDIT: Since I first made this post I've done some research and some experimentation. The methods I've described definitely work so it's one of three other things..
One: There's a problem with syntax somewhere. If that's the case we just need to find it and fix it.
Two: There's something funny going on with your files or your files names. If that's it, I can't help ya.
Three: Your browser is to blame. Most likely the iPIX plugin.
Having said that, try the link below. I've got it set up just how you described, and it works in both Mozilla 1.7 and IE 6 after I installed the plugin.
http://www.u.arizona.edu/~aef1/iPIX/swapExample.html
If it works, then we're up against one of the first two possible problems. If not, then it's probably the third, your browser/plugin. Give it a try and let me know how it goes. Oh, and be patient, if you see the iPIX logo that's good. It might just need a moment or two to decompress, depending on the speed of your system.