Unfortunately, I haven't found a way for that.
However if you've copied the Windows mail folder from a Vista machine and replaced the files in the C:\Program FilesWindows mail, you can add a custom graphic here.
Copy and paste the info inside the quote into Notepad, choose Save As, then save as ANSI format and type in backbitmaop.reg. Save it to your desktop and double-click on it to merge it intro the registry.
Quote:
REGEDIT4
[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Toolbar]
"BackBitmap"=""
You need to choose a graphic (*.bmp) that is approximately 1078 x 77 x 24 other wise it will look like a tiled image.