Best way is to get pictures from Flickr.com.
Just navigate to the site on your phone, search around for a picture you like, select the picture, it will take you to the photos details page, select the picture again and it should take you to a page where you can select the size of the image you want displayed, click on "original" you want the resolution to be as high as possible. If the photo is really large this will take awhile to load. Once loaded, long press on the photo till a menu pops up, save image, after its done downloading view the image, the phone will resize it, then hit "menu" above the optical pad, and select "set as" then "wallpaper" then crop to fit and enjoy.
Hope this method helps!