I'm sure you'll have a great time dining at the Club. As for the dress code, Club 33 currently does not have a strictly encforeced dress code, but they do request appropriate dining for a fine dining restaurant. Basically, they don't want you wearing sweats, beach wear, extremly short shorts or torn jeans. For dinner, they do like gentlemen to wear shirts with a collar (i.e. polo style shirt is fine). Many diners do dress up a little more for dinner.
If you are there for dinner, everything you order is off the menu. They do offer a prefix meal, but I can't remember what they charge for it. You should allow about 2 hours for dinner.
The Club did restructure their format for luncheon earlier this year. Salads and hors d'oeuvres are still a buffet. However, the main entree you order is off the menu (they do rotate the menu every 2 weeks). Also, I was told that they would offer dessert as part of the buffet 7 days a week (initially, they would only offer it on the weekends). I was told this last month, so I'm not sure if they implemented this.
Enjoy and have a great time!