I want to support karlcswanson on recommending the Arduino. I've used it quite a bit for little projects, as well as a field controller for a small VEX competition I arranged for my team. I'm currently working on using it as a navigation engine for FRC. Some thoughts to set the record straight:
1. The URL you posted is for the Arduino Stamp, which is probably not what you want to use. This URL at Sparkfun goes to the USB version of the Arduino board which is what I use:
http://www.sparkfun.com/commerce/pro...roducts_id=666
Notice that it is only $35, has power input, a USB program port, and a number of headers you can use to connect to a breadboard for prototyping. There is a shield you can get/make that connects right on top so that it looks just like the BS2. It can also be powered from the USB port.
2. The PCB comes with this version, and has mounting holes if you are concerned about it.
3. From the standpoint of developing a robotics platform for yourself, the Arduino has plenty of power but also plenty of room for customization. It will output a PWM signal, but it might take a bit of work to make it work with a servo. The Arduino language gives you full access to the digital outs of the ATmega -8 and provides delay functions which you can use to write custom functions to output PWM signals for servos, Victors, etc. The language is constantly being updated, and recently included support for interrupts.
The Arduino worked great for me in giving me insight into using microcontrollers and their peripherals - I definitely recommend it to a beginner since the hardware/programming/environment is so nicely put together.