If you're new to eBay, be sure and be a 'good' seller. Prep your MBP for sale by installing the system and the apps that it shipped with and include the installation disc(s) with the purchase. Be realistic about where to start your bidding - search for other computers of your vintage and be honest about the condition of your computer.
I have a number of years of buying and selling on eBay under my belt, so I knew how to attract buyers and I knew how to make sure that my buyer got all that was promised (and more - I even 'threw in' a 250GB external drive that I no longer used and specified that it was perfect for backing up the 120GB drive that shipped with my 2006 model). Most of the time, eBay can be a pleasure to deal with - just beware of anyone that wants to pay you without going through eBay.
Good luck,
Clinton