Ok, here's the easiest way (I think) to do what you want. For your phone a wallpaper should ideally be 960wx800h. For a single screen 480x800.
Lets use this pic as a test run of what I do. Save this -
http://www.portwallpaper.com/imgwal/red-mirrored-room.jpg
Ok - Now go to
.: Sumo Paint 3.5 :. (This is the online image editor I like best).
Go to > file > open from my computer, and find and select the above jpeg. This will not be in the correct size, obviously. Now go to the image menu > image size. Since it's clear that you will have excess width, let's not worry about that yet. Check the "constrain proportions" box, and set the height from 768 to 800. This will change the image size from 1024x768 to 1066x800, the correct height for your phone. From here, you could start cropping width to try to get it to the right size, but a much easier way is to go to the select menu, select all, then the edit menu and copy. Now go to the file menu and hit new image and in the box that pops up set the width to 960 and the height to 800. Next go to edit > paste, and your done. To save use the file menu the save to my computer and save as jpeg or png.
I know this sounds like a lot, but trust me, it's much easier that it was to describe.
If you need any further clarification, just let me know.