That's precisely why I've got Macs for notebooks and desktops these days.
But if the question is how to run XP on Vista-only hardware, a Mac is not the answer.
Full disclosure: even on a Mac, unless you dual-boot or install XP on the bare metal of the Mac, you can't really get to 100% native speed. Fusion is really good and quick, but there's still a couple percent of overhead. Wired ethernet network speed is one area they have some improvement yet to go.
I’ve been saying that on the Mac, you CAN dual boot or slick/install XP because Apple has made a point of making XP drivers available for all their Intel-based hardware. And they will continue to do so.