Take a look at a few of the parties listed here for some ideas:http://www.pianoworld.com/forum/ubbthreads.php/forums/21/1
Generally speaking they tend to be relaxed and fun, with everyone taking turns playing. There are usually snacks with everyone bringing something to share.
Posting like you did here is a good place to start, although you might want to mention it in one (or more) of the forums geared toward playing (Pianist Corner, ABF, etc.).
I'll try to remember to mention your post in our next newsletter too.
Oh, and if you do end up hosting a Piano Forums Party/Get-Together, remember we like pictures :-)