Thats not what you want. You want to change the flower welcome screen background. That program likely won't do that for you. That will help you change the picture when you go to system propeties.
What you need is LogonStudio Vista:http://www.stardock.com/products/logonstudio/downloads.asp
Make sure you get the vista version. Yes I know you have Windows 7 so before you ask, yes it will work. I've used it on Windows 7 and it works fine. Once installing and opening you will be given a few preinstalled logons. You can make your own by using your own background image if you like. The program will stretch it so its best to get one that is already sized to your resolution. You can also download more from
www.wincustomize.com. You don't need to have an account with them to download the logon screens. There are hundreds to choose from.
Just click apply when you've found the one you want.