To answer the last poster's question about Ethernet shields, I use an ENC28J60 based shield from Nu Electronics (www.nuelectronics.com). This can be picked up from them, or on eBay, for 1/2 the cost of the official ethernet shield. I think if I were to do it again, I would get the official one, as I spent 3 weeks hacking together the poorly documented example code to get something usable for me. It doesnt use the same library as the official shield.
As for what I use it for: I use it to log data from my tracker to a MySQL database, via PHP scripts. This lets me log data very easily, and once you have it pushing to a database, you can do anything you want with it. My demo (as I am learning PHP and MySQL very recently) is at http://solar.panicdog.com
The trouble I am up against is the Ethernet shield and the AdaFruit motor shield I am using, are running on conflicting pins. I will start another thread to discuss this, as to not derail this topic. If I cannot resolve the conflict I may have to run the two shields on different ATMega328's, and have them talk on the I2C bus (which I'll be using in this project anyway, so not a problem I suppose).
Yes, edit your first post to change the subject to something like "need help with Adafruit motor shield and ethernet shield". That way it's immediately obvious what you need help with.
As far as I can see there's very few pins in conflict between those two shields. Pin 10 (digital 10 or D10) is used as CS on the ethernet shield and it's a PWM output for the Adafruit shield. Not every pin is capable of PWM but every pin can be used for CS.
The kicker is the Ethernet shield uses the SPI header in the middle of the board and the Adafruit shield doesn't pass that through to shields stacked above it.
So stack the Adafruit shield on top and clip its pin 10 off, so it doesn't go into the Ethernet shield. Then solder a jumper from 10 to any other free PWM pin, like pin 3. If you don't have a soldering iron yet, just bend the pin out and wrap some wire around it. Jam the other end of the wire into pin 3.
Change the software to use pin 3 for the motors. That should be relatively easy.
It does look like the Adafruit board has holes for a 2x3 pin header to pass the SPI signals upwards. If your shield doesn't have that header, you can buy one and put it in to stack the other one on the top. It doesn't need to be soldered.