music editing software

I typed in the title and it automtically gave me some similar threads (which I like) but didnt know for sure if they did what Im looking for...
To start I have
xp vista and windows seven
dual core on one and pent 4 on the other
good amount of ram in each
and good hds

I want to get a free program where I can take a few to 30 seconds of each song and make a full track out of the collections, I am going to make a light show for christmas and other holidays with automation pcs so at the right given times certain things move or turn on etc.. thanks for any help on this.