Started this last night, finished up this evening on my '03 non-S boxster.
The oval tip comes off by removing one 13mm bolt.
I used a 7/8" tapered bit, so the holes I wound up with are quite large - 7/8" by about 1.25 or 1.5" because of the angle at which I drilled.
I have not had a chance to open the throttle up properly - rolling on my spare right now, as I picked up a nail on the way to work today - but once I get a proper tire on, we'll see how it sounds. It currently reminds me of the Injen catback I had on my Tiburon, which I loved dearly.
The best part about this 'mod': if you hate it, pick up a used Boxster muffler for $50.