You might want to try this link to my help page on Working With Bravenet Templates. The page on Template Editing has links to several good free web page design applications.
Another resource, on using Templates from the Template Gallery, is the May 25,2007 Newsletter. You can find it in your Bravenet Account Manager under "Resources --> Bravenet Newsletters". Their recommendations are Photoshop, GIMP, and Paintshop Pro. But other programs can be used.