Ok. Now you have your sprite. Now what?
I usually use Paint, since it's easy to use and comes with just about every computer out there (sorry to you Mac users, I'm a PC person!). Some people use Gimp or Photoshop, but I'm not a computer genius, so I stick to what I know.
Most sprite sheets I know of have weird color backgrounds, so once I've imported the sheet to Paint, there's a small amount of clean-up that has to be done.
You have a few choices. You can either find an online cross stitch program, buy a cross stitch program, or enlarge the pic, print it out on a color printer and try to eyeball the colors.
If you're wanting to get an online program, a good one is KGchart. It is simple to use, and it tells you your thread colors! ^_^ For a list of other chart programs I defer to the wonderful folks at Sprite Stitch. Also from Servotron at Sprite Stitch a wonderful 'how-to' on KGchart.
For those of you who just want to print it out and so on - here's how I do it.
Step 1: Enlarge the sprite - it makes it easier to see.
Step 2: Figure out how many colors it needs.
Step 3: Make a color grid going from darkest to lightest.
Step 4: Print and go shopping.
After that it's easy. One square equals one stitch. 14 count is the most common fabric (at least at my store) which means 14 stitches to one inch. The Octorok is 15 x 16 stitches. Perfect as a bookmark design or a magnet. (It's still 9 colors and 174 stitches in total so it will take at LEAST an hour for beginners.)
There is some argument about using white in a sprite vs. stitching on a white surface. Personally I don't always use white fabric, so I always stitch it in. It give the sprite a solidarity, and there's no holes in the middle of the pattern. Although if you wanted a slight 'relief' look to it, or if there is a background color that there is a LOT of (like the blue in Super Mario Bros. World 1-1) then not stitching may save you on thread, patience and sanity.
And that's it, you've got your sprite, you've got your pattern - now go and get your supplies and voila! You have a happy self/boyfriend/girlfriend/husband/wife/friend/significant other/WHATEVER!!! ^_^