Javascript. There are loads of free slideshow scripts. First one off Google is barelyfitz.com/projects/slideshow/ Which looks ok.
You could also try Hotscripts, there are probably some off the shelf PHP implementations there as well which you could tie in to a data source.
Or you could go uber trendy and find a Web 2.0 solution using Ajax. Make sure you put some rounded corners and drop shadows in though, or Tim O'Reilly will come round your house and kick your cat.
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