Well while you are "selling" software development. The reality is that you don't want to sell software development. Your job is to give a good overview of the craft so that kids who have an interest in it will learn more and maybe some who aren't interested will become interested. You need to represent programming accurately.
Some will have unrealistic expectations about programming and will want to enter it for the wrong reasons. You don't want to sell them software development. You want to make sure that they have a better idea of what it is. And if upon learning that they decide to pursue something else, then you have done a real service for both developers (who have to deal with a bunch of people who should not be here) and the students (who don't end up in a job they hate).
Programming is about communication. Try to find someway to mention this. Constantly the requirements are changing and the customer doesn't know what they want but through communication you have to find it. The stereotype of the kid locked in his office programming all the time needs to somehow be deflected.
Programming is about problem solving. Not all kids are interested in it. But for those that do love solving math problems/etc. who will probably go on to software development, engineering, mathematics, etc. you have to make sure to represent that programming is about problem solving.
Okay here's the practical consideration. Kids like games. As a kid I learned this thing called BASIC and then later this thing called C all to muck around with games. Kids also like bells and whistles. The old days of for loops in QBASIC making circles and lines that grow from a tiny dot to taking up the whole screens, often with annoying music going from low to high via a for loop....they respond to that.
So basically the reality is that you can find some practical examples like showing off some relevant "cool" iPhone app and discussing how that was programmed. You can mention how it takes programming to guide the mars rovers. And all the standard stuff to make the geeks drool. Then you can discuss games and maybe even show an example of one that you did.....
The reality is you don't want to sell House who is going to become a doctor to go into Software Development when his heart is into being a doctor. You want to sell Richard Stallman, Linus Torvalds, etc. that they want to be a software developer. And for people on the fence you want to educate them a bit more so some of them can realize software development is not for them and others can realize that software development is for them.
One of the best things you could do would be to give them a CD (that works on windows computers because that is probably what they have) with some programming environment and some sample programs so they can play around and see for themselves. I don't know what the best answer is. Maybe Python and find an open source game or Java and find an open source game. Most will probably throw it out. But for the one or two who are interested they will get that cd, load it up, install the JDK, play the game, and start asking questions like (how do I stop myself from losing life if an enemy hits me, etc... [I still remember modifying that qbasic centipede game to make me invincible whistle].
So I think the reality is this:
1) Dazzle them with some cool real life examples of what programming can accomplish
2) Give them a sheet with web links and resource to learn more, along with a cd with some type of quick environment that they can use to play around if they want. You'd be surprised how smart kids are. If I had the computer I probably could figure my way out at 7 or so. These are high school students. The more technically oriented ones are probably already fiddling around with some programming language. But there may be ones on the fence. And I'm sure the more technically oriented ones would always appreciate new ideas.
3) Discuss games...in high school it was all about the games. My friend who used Turbo Pascal to make a space fighting game was pretty revered :) The rest of us were all into text games. Basically many of the would be programmers will be game obsessed by that age :-P