GRRM’s appearance in Second Life on the 31st, at 9 PM EST, will be syndicated by a number of affiliate sites in-game to deal with the fact that locations can only carry up to 60 people at a time. You’ll be able to listen to the proceedings (which will feature a reading by GRRM and then a short Q&A) through these affiliates, and submit questions via IM. To find out more, including a list of the affiliates, see here.