Hiya
You won't need the master disks, it'll be on your hard drive somewhere. I don't know exactly where the file would be.
First of all, look in display properties - assuming you're using Windows XP, right-click on a blank area of the desktop (i.e. anywhere else apart from on an icon or the taskbar), then click Properties from the menu that appears.
Then, click the "Desktop" tab at the top. If the Packard Bell picture is not listed in the list of pictures here, you may have to click Browse to find it. It's more than likely to be either in C:\Windows or in a folder within there.
If you can't find it, you can click on Start --> Search and search your "Local Hard Drives" for all pictures. I've disabled the search wizard on my PC so I can't tell you exactly, but I think if you search for all files and folders and put the following in the search box:
*.jpg;*.jpeg;*.bmp;*.png;*.gif
It'll work through and show every picture file on your PC! Alternatively you could try searching for "packard" which may turn up something, depending of course on what they called the file originally.
And in worst case, even if you can't find the exact Packard Bell image, you might find another one that you like better