Paypal Flash Button Enhancer - description from Softdepia.com:
This program creates the code the Flash buttons being sold across the internet use to inform Paypal of the products information.
The added bonus is that it supplies the code necessary for all the options that Paypal offers such as a cancel page, changing the color of the page to black instead of white and other options currently not available to most of the Flash buttons users.
Now you can have these options as well. We have tested it with several different varieties of the paypal flash buttons and it has worked with all of them.
Paypal Flash Button Enhancer is a "Free to try" program. You can download and try it for an evaluation period.