Can I make a process run in background?

Hi, Before I start explaining my problem I'd like to say one thing: I'm aware that php isn't the best-suited language for what I'm trying to do (an IRC bot), but unfortunately by now it's the only way I have for various reasons; I want the bot to run a process in background (a periodic message, for example) while listening for events (like a user joining a channel or using a certain command) and consequentially executing the corresponding functions, is it possible? and how? if it can be of any help, I'm using a (pretty old) PEAR library of irc functions named Net_SmartIRC Thanks, Luca