Ok add a picnik.com sideshow to your google site which continually loops, does not link to your photo album and auto starts when the visitor accesses you page. Go to picnik.com and create your slideshow, then click on share, select your size and copy the html code.
Go to the page on your google site where you would like the slideshow to appear > edit page > insert > more gadgets > featured > select embed gadget > paste in the html code > customise the gadget by unchecking the title box > also change the size of the gadget to the size of your slideshow, to get the size carefully read your pasted in html code and it will tell you the height and width!
Remember to save and you're done. Let me know how you get on.
(Here's one working ... http://www.lacasafrancestina.co.uk/spiritual-retreat/facilities)