I will like to present to you my quadruped. I'm using an Arduino Mega and a servo controller SSC 32.
I'm also writing a blog as I go along and I invite you to visit it. Hopefully you will find some useful information.
I have a couple of articles about Inverse Kinematics (with arduino code) and I hope I will publish more interesting articles as I make progress. See link below to my blog:
Next, you might try implementing a crawl or creep gait. This means moving only 1 foot at a time.
Assume a stable tripod on 3 legs, step forward with the 4th leg, and then swing the body forward
using the other 3 legs, so you get a new stable tripod for support, and can lift and step the
rear-most leg.
If your servos are a little weak, the creep gait will work better than a trot [2 legs by 2 legs], as
there are always 3 legs down and supporting the frame.
Battery, 7.4 Volts can kill your servos, I would suggest either buying a BEC (R/C world) or finding a similar way to reduce your voltage to 5 volts . Depending on the number servos and amp draw a basic R/C BEC should handle your requirements. Any R/C shop should carry the Castle Creation Brand, or a suitable substitute, they have both a 10 and 20 amp version. If you go 20 amp you will have to replace the supply side wires. You will also need a small fan to provide airflow as the R/C ones are assumed to mounted on a rapidly moving object.
Other than that I liked your explanation of IK, it was a lot clearer than a lot of the ones I have read.