[Spaceman Spiff]

www.evite.com is your friend. Not sure about linking to your home page or anything like that, but it works great for me. You can limit the number of people allowed to attend and also allow or prevent the invitees to invite more people. It won't stop people from subverting the system and still bringing what I call "surprise guest stars", but if you make it clear that signing up through evite is the only valid way of saving a seat, it won't take long for them to catch on.