Sean,

Keep in mind that LEDs should be run off of a constant current source. This kind of power supply provides a fixed amount of current and varies the voltage as needed to maintain that current. It's used with LEDs because as they heat up they draw a higher voltage so you need to limit the current to keep the voltage in check.

One problem you are going to run into is that if you run chains of LEDs in parallel you will wind up with unequal current going down each branch since the resistance (and hence voltage) of each LED varies. If a LED burns out and you loose one branch it will greatly increase the current going through the other branches.

For higher power (350mA+) LEDs I'm a big fan of these current sources. They sell models ranging from 350-750mA and I've had two in my truck for over a year with zero problems.
http://www.dealextreme.com/details.dx/sku.13557

Since your LEDs draw a relatively low current one option would be to simply put a resistor inline to drop the voltage and leave enough of a buffer with the current that you don't burn them out. If you run a single resistor per trunk of 5 LEDs it will allow for more equal current distribution. Alternatively you could use a LM317 (or a low drop out substitution) to make a current source.

- Matt