Before you buy the first set of shiny wheels that catch your eye, be sure to understand offset and how it applies to Boxsters. Do a search here on 'offset' and 'wheels' to bone up on other's experiences. There are plenty of threads of people who buy or want to buy 11" rear wheels and want to know if they'll fit on a Box (they won't). Also plenty of ads on ebay for wheels that say they'll will fit Porsches (but might not necessarily fit a Box unless you want to use insane sized spacers). Porsche wheels are
very spendy (please be seated when looking at prices), so you don't want to make an expensive mistake.
Another item that has to be considered is what size wheels do you have (17", 18") and what size do you want to go to?
Lots of questions that need to be answered before getting out the credit card (or taking out a loan - some sets can cost $4K
).