[TheLastSuperman]

^ Please post a link as Lynne asked. On a side note though, some forum designs meaning... if you have to 728x90 banners and you want one on the left, and one on the right w/ a little spacing between them without realizing that their forum is a fixed width at 980px - this won't ever happen! So make sure that you're either using a fluid style or that your set site width is large enough to actually hold both ads if you have them side-by-side.

980px-728px=252px minus any padding or margin settings to play with.

^ Very rough example but you should get the idea, if simply stacking ads top to bottom it shouldn't matter unless you just don't take it into consideration.