When I was in college, I envy Google Summer of Code for being only open to university students. Maybe it might have indirectly influenced me to get into the university ;). Anyway I ended my envy later by participating in GSOC. If you are also a college/high school student under 18 years and have such envy as I had, then here is a news for you ! Google has announced "The Google Highly Open Participation Contest".
This can be called as the pre-university version of Google Summer of Code, where the objectives are similar - to get involved youngsters to contribute for the open source projects. Here you will have to work on tasks of the 10 listed open-source projects and you have to complete them by 4th February 2008. So I guess timing is perfect as you will be free from your school work in the holiday season. Also attractive prizes are on tray for successful participants. You will receive a certificate and tshirt if you complete a task and you will be paid $100 for every 3 tasks you complete. The 10 grand prize winners will be selected and will have the opportunity to have a paid trip to Googleplex (wow!)
If you are considering to participate, then I would like to recommend you the project, SilverStripe CMS. SilverStripe codebase is purely XHTML, CSS, JavaScript and PHP5 based, so you will not require a high knowledge to start hacking. Also SilverStripe is a cool project which has lot of potential and you will be delighted to be part of such elite community ;). From my summer of code experiences I can tell you that the SilverStripe got very friendly community, so you will never run out of support. Have a look at SilverStripe's tasklist - http://code.google.com/p/google-highly-open-participation-silverstripe/issues/list. You will notice there are variety of tasks such as testing, designing and documenting where you don't even require programming skills.
Anyway if you are considering to be a GHOPer under SilverStripe I'm more than willing to help you in whatever the ways I can. Get in touch with me.