My friend and I are both pretty geeky, especially by comparison to normal people. We can both poke around in CSS, and set up a simple CMS. As far as code goes, that's the end of it though. We plan on working with developers, leaving the actual coding to them, while focusing on the overall flow and design of our site/apps.
How many other applicants are in the same boat?
I would personally recommend picking up some Python and maybe Pylons and start hacking some webapps (others might recommend Ruby and Rails, etc). How else are you going to build a demo from the 15k that YC provides?