I trust you just as much as anyone else I don't know.
Sorry, it's just that downloading wallpapers and screen-savers are 2 of the fastest ways of picking up adware, spyware, and other unwanted programs.
McAfee Site Advisor is free to download, and it will tell you if a site has been tested. Once it has, it will report any problems that occurred in their test computers, and mark it as a Red, Yellow, Grey or Green site. If you stick to "Green" sites, you'll never download anything that can harm your computer or slow it's performance. It even puts a colored check-mark next to each match on a Google search, so you don't even have to open the web page to find out if it's safe. Personally, love it.
If anyone is interested, it's http://www.siteadvisor.com/download/ie.html
or just Google "McAfee Site Advisor".