Have you added the other banner and maybe gave them weight? I am a Windows guy so I have never used PHP. But usually most scripts come with some instructions. Most ad scripts come with Zones and weights of the banner / user.
Hey If you have only personal banners then phpadsnew is highly an overkill, it needs lots of resources, Just get a simple php ad rotator, You will get it working in seconds. Use phpadsnew only if you are selling your inventory to others.
php ads new is great I use it on my site too. I could sit here and tell you step by step how to set it up but I don't have the time. They do have a nice manual on the site that you can d/l... I spend about an hour looking over the manual and then another 30 mins setting up my banners. Once you get it set up it is a great script.. I use my invocation code on a few other sites too. I just update the banners in ads new and the rest of the sites get updated with no hassle at all. I have heard that is was a resource hog before, but I honestly have not had any problems with it.