Multiple chat rooms, technologies and server load,

I am working on a website where I need multiple chat rooms. Each room will be generated and tied to the content/event just generated by the user and will aproximately last 15 minutes and then autodestroyed. One room will contain aprox. 15 users. Many events will co-exist at the same time.

I have been googling around a lot recently looking for the most appropriate but still easily implementable solution. What I came across are three main paths:

1. using a mysql-php ready made script (ie. phpfreechat, x7 chat)
2. using irc channels created on the fly through an ajax or flash web frontend embeded as an iframe (lightirc, qwebirc, mibbit, (advice more if u want))
3. using some lively generated hosted chatrooms (ie. everywherechat.com, gabbly (i really need to know more of those, again, advice if you can).

Still I have many doubts on all this: irc frontends cant be customized as much as I'd need (ie. disable kick or ban functionalities). Php-mysql solutions, on the other hand, make me think there will be a lot of server load concerns with such a big user-base.

I am on a paid but non dedicated hosting plan. Php memory limit set to 64mb kind of stuff. How many users at the same time would that hold? Hosted solutions are the easiest ones, but can you recommend one that allows rooms to be created on the fly by just passing in some parameters? (no regist开发者_运维知识库ration, just a quick-easy-flying chatroom).

I know many of these questions are not strictly programming related but more technology related. But still a programming related answer could help me sort out the right direction. So your contribution is really appreciated. Thanks ! Sorry for being long