Just checked those links and all of them seem to be broken. Spriteart.com seems to work, but I can't find anything on tutorials or whatnot. The second set of two don't exist anymore.
However, some searching provided some other sites with teaching goodness:
- A 10-step approach to doing some sprite work.
Mark's Pixel Tutorial
- Covers most of the same material as Derek Yu
- A good tutorial for doing things like floor tiles and such.