It is incorrect to say XP Service Pack 3 has been tested with Vista - it has nothing to do with Vista.

In fact it's incorrect to say that Microsoft have launched XP Service Pack 3 since it is not out yet, officially due "2Q 2008". They have (yesterday) made available on Microsoft Downloads a document (not really worth the paper it might be printed on) outlining what will be in XP Sp3 but that's all.