Hoser, you've opened up two BIG cans of worms with this post. Tires and Oil. Sheesh!
1. Tires: Do a search on "tires" and you'll find page after page of what people like and dislike on this list. My advice is to buy as good a tire as you can afford, and remember that the rear tires will wear out quickly due to the camber settings. I have decided to go with Sumitomos because they're cheap, look good, last about as long as other brands, and ToolPants has them on his Boxster and he's my hero on this list and Renntech. If they're good enough for him, they're good enough for me. Conversely, you'll find that many, many other Boxster owners here like other brands for various reasons and none of us have a favorite, but we sure do have our gripes about rubber we've put on our cars in the past! BTW, I'm currently running Kumhos and they're not bad, but not great. They're very slippery in cold weather here in Houston (45 degrees or lower), but then again, high speed summer tires will be that way.
2. Oil: Same thing, do a search and you'll find more strong opinions. However, most use Mobil 1. The real debate is viscosity... Porsche recommends 0w40 Mobil 1. It's hard to find though and expensive when you do find it. 5w40 can also be used if you don't live in the North, it's found most everywhere (Wallyworld, Kmart, etc.) and goes on sale all the time. Just be sure not to run mineral oils in your boxster. That's a no-no.