well lucky for you, you have a whole year to get ready! And this is the time to stock up on Christmas lights while they are half price too. Here are the first 2 steps listed on the website below. It has all of the basic instructions, and also a forum where you can ask questions. Good luck!
1. Decide how big you want it. A channel is a unit of lights that can be controlled individually. For example, a single bush in your yard may be a channel. All the lights in a channel work as a unit (you can't flash an individual light bulb). 32 to 64 channels is a good size to start with.
2. Stock up. The best time to buy lights is the day after Christmas. Many times you will find lights that were normally priced around $2 a strand fall to $0.50. Check out Wal-Mart, Target, Lowes, Home Depot, K-Mart, etc.
Edit: oops, just noticed that this is the same website listed in the answer above. Probably because it is the first one that comes up on a google search for how to make Christmas lights flash to music. So I have found an additional site with a video that looks quite helpful:
http://www.howcast.com/videos/714-How-To-Make-Music-Controlled-Lights
Also, here is one at ehow that has some good ideas on planning it out on paper in advance: http://www.howcast.com/videos/714-How-To-Make-Music-Controlled-Lights
And this one, using hair gel of all things! It claims to be able to show you how to make it go in time with the music.... http://www.metacafe.com/watch/1917245/how_to_make_light_music/