Load simulation tests

Hi all, I was wondering if there were any ways to simulate loads on a PHP script running on the server? Basically, I'd just like to take one of my sites through a dry-run so to speak and simulate x number of visitors. Ideally, I'd prefer something that didn't have to be installed on the remote server. Also, it would have to be something I could use from within Linux, as I only have Windows running as a VM, and I'm not sure it would work as intended if run though a VM. Have any of you used such tools, and if so, are there any you'd recommend? Thanks, Ash http://www.ashleysheridan.co.uk