Hunting is a blast. Do you know the hunt club you will be hunting with? You will need to go as a sponsored guest. Some hunt clubs are more private and not as welcoming as others. If they have a web site, you can probably contact a staff member. I'm sure someone will be happy to help you. I know our local club is always looking for new qualified (good rider/safe horse) members.
Your horse needs to be fit to hunt. The later in the season, the longer the hunt will be. If you haven't been trotting and galloping multiple miles, I would advise not to hunt until your horse is fit. You can probably get your horse fit in 6 to 8 weeks of work. If your horse is not fit, you run the risk of injury to both you and your horse. A drag hunt is usually fast and very fun.
Your horse needs to be GREAT on the trail with a group at WTCG. Quiet, obedient. You need to be able to jump outside quietly.
The best way to get your horse accustomed to the hounds is to offer to work hounds with the group (if the hunt does that). You'll go informal and exercise the hounds. That way you can judge how your horse will behave at slower speeds (usually just trotting). Our hunt would then go on a fun trail ride through hunt country after the hounds were put away.
For a hunt, there is some etiquette you'll need to know, such as staying at the back of the hunt, since you are not a member. Dress formally and conservatively - dark coat, beige breeches, white shirt with stock tie. Everything should be clean - like you're going to a show. You'll need to keep a low profile and keep your horse in good control. Don't pass anyone with colors (on their hunt coat lapel). If you do well they may ask you to join. It is great fun.

Good luck and tally ho!