I am not sure how paypal cart works to be honest.
You can create your own headers using photoshop etc.
Make sure you have the sizing correct etc, and then give it the same name as your current header file and simply upload via ftp.
As for actually creating it in photoshop it all depends what you are after?
There are some good designers are here who could do one for you.
a GOOD HEADER MAKES ALL THE DIFFERENCE!
Have a word with nick or Dezina
