Changing your wallpaper or screen saver:

Start -> Control Panel -> Appearance and Personalization

The first section called Personalization would be the only one you would actually need to use to change the wallpaper or screen saver

Changing the font/background or signature to your emails in microsoft outlook for microsoft office 2007:

Open your email (Microsoft Outlook) and click on Tools (will be in the main menu at the top) then click on Options. Then click on the Mail Format tab. From there you will able to change/adjust your signature, change the font, change the stationery, and more