Check out Perfectlap's new seats:
pics of New Wheels and GT3 Seats
Pretty tight huh?
I haven't replaced the sets in my Box, but I have taken them out before. I have replaced seat in other vehicle's before. You just have to make sure the mounting holes line up, or use of fabricate a mounting bracket.
One thing to watch out for on the Boxster, is makes sure you disconnect the battery before removing the driver seat. There is a plug under the drivers seat that if removed with the battery connected will cause the airbag light to come on, and it won't go of unless you go to a Porsche dealer or someone who has the PS tool of some sort to reset it. (also have your radio code handy!)
HTH,
Larez2