Right click on Panel then pick Properties ("First step.jpg")
Background tab, Background image and load one of pictures I give you ("Second step.jpg")

Suggestions
Find Gnome theme Win2-7(Pixmap)

Install Emerald window manager and find good Windows 7 theme
Install Fusion icon, start it and change window manager to Emerald

Install DockBarX

Install GnoMenu, Find "True 7 HD" button and "Windows 7" menu and load them all.