hey mate... I use phpAdsNew... it's a seperate application [free] that you install to your server. it allow you to manage ads for different users, have them rotate, have some shown more than others, etc
you can check it out at my forum if you wish.
http://www.commodorelife.com/forums/
I currently have 2 rotating banners. and they appear below the main banner and above the navbar
PM me if you want more information on this program, it will be a little hard to explain in a post. but I can do a little rundown in here for other people that use this thread as a reference