By the way, my example was the "hand coder method". DW also has a built in method (a behavior called "Swap Image" which you access from the Behavior panel). To use that method, you would click in your trigger link (in Design or Code view), then in the Swap Image dialog that appears, you would select the target image that you want to swap out and use the Set source to: field to browse to the incoming image). Select the two options below that field and click OK, and you are done.
And I definitely agree with Nancy about the use of tables.