If you look at the background of Internet Explorer's toolbar, you'll see a very low profile bitmap. You can actually change this bitmap just like you can change Window's background (well, maybe not so easily!).
Run "Registry Editor" (Run "RegEdit.exe" or "RegEdt32.exe")
Select:
HKEY_CURRENT_USER\
Software\Microsoft\
Internet Explorer\Toolbar
Run "Internet Explorer"
Select "View | Options | General"
Uncheck "Background bitmap" checkbox
Switch back to the Registry Editor
Add following parameter as a "REG_SZ" type:
BackBitmap
Value of the "BackBitmap" parameter should be set to the path to your bitmap (C:\WINNT\SETUP.BMP for example)
Switch back to "Internet Explorer"
Check "Background bitmap"
Click on "OK"
Now you should see the newly specified bitmap on your Internet Explorer's toolbar.