Adobe has released a PDF document outlining compatibility of their products with Mac OS X 10.5 'Leopard'.
Both flavors of Photoshop CS3 are compatible with Leopard. In fact, most of the CS3 line are compatible, with a few exceptions.
Lightroom requires an update, but they do not provide any details as to what features are not working properly (or when the 'future update' will arrive).
"Photoshop Lightroom 1.2 is not fully certified for Mac OS X Leopard, but future updates will address areas of Leopard compatibility".
Bad news for Photoshop CS2 (and earlier) and Photoshop Elements 4.0 (and earlier) users as they are marked as "Not Designed for Mac OS X Leopard". Comments state "Likely to encounter issues for which there is no resolution."