Using Drupal 6, LiteJazz theme.

I can't program so I came up with this solution. I wanted to modify a theme header which is one section(full width), into three sections horizontally across. The center and left sections would be used for advertisements.
My Solution, create an HTML sized rectangle (maybe a table), with outlined boxes in the center and left as place holders, into which I would assign the customer's ad. The whole thing would be saved as a graphic image which would be assigned to a new block placed into the Header. I know it is not dynamic as far as changing out ads, since a whole new banner graphic would have to be prepared with new ads, but these ad slots are to be sold for extended time periods, min. 6 mos.

Please give me some feedback thoughts.
What format would you recommend to save the pasted up banner graphic in?

Thanks
Paul