Hey programmers I need your help.

I am trying to develop an app for facebook.

I dont know how best to explain this but I will try my best.

I made a design on Photoshop. I intend to sell that design. But I also want my potential customers to be able to edit a small part of the design to make it customizable.

I want to create a small text box where my customers will typr in whatever text they want to put in the editable area. Then the text will then be formated according to the design and placed on the editable area

How do I acheive this and what program do you recommend I use. I know its a very simple thing but I have no idea how to go about it. I like to code so I am not afraid to get my hands dirty.

Just a few pointers is all I need.