Windows XP trounced Windows Vista in all tests, regardless of the versions used or the amount of memory running on the computer, says Devil Mountain Software.In the latest Mac versus PC ad, that put-upon Windows guy quietly concedes he's "downgrading" from Vista to XP. He may have good reason: new tests show that the older XP runs common productivity tasks significantly faster than Microsoft's newest operating system. Researchers at Devil Mountain Software, a Florida-based developer of performance management tools, have posted data from their most recent Windows performance tests -- and Vista, even after it's been upgraded to the new...