You have been charged with attempted copyright infringement
Grant Robertson's The RIAA vs. John Doe, a layperson's guide to filesharing lawsuits is a great read if you ever wanted to learn about the RIAA's heavy-handed tactics for suing P2P users. Robertson revised Ray Beckerman's legalese filled How the RIAA Litigation Process Works in order to present a more interesting, accessible overview.
Take a look at some of the comments, too. For instance, Song.mp3 points out how utterly unreliable it is to base a lawsuit on an IP address. How many people are using routers? Most will be configured as firewalls, and the IP points to the router, not the computer. If the router is configured as an open access point, anyone within wireless range could log onto the network and be using it to share files.
All of this got me to wondering. IANAL, but the lawsuit seems to be based on the RIAA's ability to download the files as proof of copyright infringement. How could they know if anyone else has downloaded any files? (I'd be curious to know if ISP's are maintaining and suppplying full IP traffic records to the RIAA) Is it copyright infringement to redistribute copyrighted materials to the copyright owner (the RIAA is the legal representative of the copyright owner)? At best can the RIAA only claim that there is attempted copyright infringement? Regardless, it must be impossible to prove that there was any real damage done the copyright owner if the RIAA can only show themselves to have downloaded the file.
Now I'm done. Rant about other idiocy--Blackboard and patents--coming in the near future ;-)