johno12345: They won't stop you from taking 45 before 41. But it probably isn't a good idea. It's OK to hold off a quarter on starting the physics sequence; you can use the extra time to get other things out of the way (PWR, GER's, other prereqs) or take something that just looks interesting.
frog139: If you still feel comfortable with the AP C material, you can start straight in at 45 in the fall and move on to higher level classes (or take care of GER's) in winter and spring. If you'll do that, you'll also need physics 70 at some point, as superwizard refers to. Your other option is to take the 60 series (the whole thing; they don't let you skip any with AP credit). There will be some material you've already seen, but I promise you will never be bored.
Introsems tend to focus on a very specific topic that you wouldn't hear much about in other courses. The topics are also often of some special interest to the professor--an area of research or expertise, or sometimes even a hobby (the most well-known being Nobel-winning physicist Doug Osheroff's seminar... on photography). Note that you have to apply to get in; some are more competitive than others. Don't be afraid to apply for a sophomore seminar as a frosh, or vice versa.
masterharper: There's a class called "Intermediate-Advanced Hip-Hop" offered in the fall, but I don't know anything about it.
For everyone:
AFAIK, the hardest activity classes to get into are the social (i.e. ballroom) dance classes. If you sign up shortly after enrollment opens (or for this quarter, as soon as you meet with your advisor) and go a little early on the first day, you should be fine. By the way, everyone should take at least Social Dance I sometime in their Stanford career.
About your advisor meeting: Unless you really have no idea what to take, you should go in with a short-ish list of potential classes and ask for your advisor's opinion on those. Don't start from scratch at the meeting. And make sure your list isn't just prereqs for your major--it's important to explore a little, especially your first year.
Finally, have a look at stanfordcourses.com. It's a much better search tool than Axess if you're browsing for classes.