If you are planning to submit the final images as stock, I don't think you can use a third party office backdrop. You would not own the copyright to the image used to make the backdrop, so you would not be able to sell the images.
Jbarber is right (as usual
). The way to go us use a green screen, or shoot isolated over white, and put in your own office background that you have shot yourself.
Lisa, (as usual) is more right than me. I was so caught up in where to get back grounds that i forgot about copyright. They are, however a great resource for an assignment job. Painted backgrounds create a completely different look from reality. You should check out the links just to know about them. Oh, and they cost a lot of money to rent.
