If you have installed GotBanners and if it displays only one columns of banners, here is your solution. I started getting a lot of mails asking me how to do it. So, here is the answer. Its fairly simple.
It purely depends on the space you have. You need to have atleast 290px width to accommodate 2 rows of 125×125 banners. Because, GotBanners automatically adds 5px margin to each banner. If you have lesser space, alter this line in gotbanners.php :
echo "<style>.gotbanners { text-align: center; } .gotbanners img { margin: 5px; } </style>";
Change the 5px to something lesser. If you just have 250px, you’ll have to change it to 0px.
Hope its clear for everyone. If you have any other questions, feel free to contact me.
Jason 
akash 
Well since GotBanners plugin supports HTML what do you say about simply adding br at the end of each banner