Shouldn't be a problem, as that's how we currently have it set up - for them to appear in a random order.
I've installed OpenX on my sites for a number of years now and love it! Really hard to understand the concept at first and took awhile to get the first ads up and running but once they're up and running, it's great! I've used it to great a login for my advertisers as well so they can track how their sponsorship campaign is coming along. It's really useful and great for adding new ads, new advertisers or affiliates. I even use it to send notices that otherwise might get missed.
