I did this for my speed-freak DH last year (speed as in "fast", not the drug, lol).
I too was worried about him finding out before I wanted him to, so when I made the reservation (about 6 months in advance) I told them not to send the paperwork until after Christmas, because that's when I would tell him about his surprise.
I don't remember how the charge showed up on our statement, so I can't help you there. If you think your DH would see it, maybe you could use a money order instead.
The way my DS and I surprised DH was to wrap up a little "Hot Wheels" style car with a homemade "gift certificate" that I made on the computer, and we gave it to him on Christmas Eve. He loved it! When the official paperwork did come, it had a gift certificate in it, so if you wanted to use that one you could, but you would have to make sure that you got to the mailbox before your DH.
The Driving Experience itself was wonderful! They only schedule it a couple of days a week, so make sure to schedule it as early in your trip as possible. That way, if your first "reservation" rains out (like ours did) you'll have a little bit of flexibility to reschedule for later in your trip. If it rains out and you can't fit it later into your schedule, they give you a certificate good for up to one year later at any participating track.
The entire experience takes about half a day. While the drivers were in their class, the crew took the kids around the track in the van for a couple of laps...they went pretty fast too! My DS (6 at the time) loved that part, and he got such a kick out of watching DH drive. It was pretty funny, because everyone in the class had their own little "cheering section" with them, and when they finished driving and got out of the car, their group would cheer and clap, and the driver would be beaming from ear to ear like a kid. All the other drivers would slap them on the back, and then they'd all stand around comparing lap times. So much testosterone! All the wives were standing around, with our cameras and camcorders, filming them. It was sort of like you'd do with your child, lol.
They have a little graduation ceremony at the end, where they get a certificate with their lap times and average speed.
If you get the Orlando Magicard (free), you'll get a 10% discount.