I cannot recommend a tire, as I just recently purchased my 2002 Boxster S, from Don Rosen Porsche near you. As for where to purchase the tires, I heartily recommend
Tire Rack. As for where to mount them, they have a qualified installer program. The qualified installers are supposedly reviewed and approved by Tire Rack. Personally, I can Recommend I. Service in Cherry Hill, NJ. Its only about 6 miles from Philly, speciallizes in German, Italian, Japanese and Swedish high line car repair and is very competent. I have used them when I bought tires for my NSX and RX-7 previously (through the Tire Rack). Besides, just going there you get to wander through any number of Porsches, Ferraris and other exotics in for service. Good luck on your purchase!