http://knol.google.com/k/electronic-circuits-design-for-beginners-chapter-8#

As the Arduino pins supply 5 volts and your valve requires 8 volts I would suggest using the Arduino to control a transistor supplying the 8 volts to the valve.

You need analogWrite.

http://arduino.cc/en/Tutorial/Fade

http://arduino.cc/en/Tutorial/AnalogReadSerial

See this.

http://arduino.cc/en/Tutorial/BlinkWithoutDelay

Hi... I built the parallel programmer and it´s working fine. I only use it to bootload chips on a breadboard but loading sketches should be as easy.

Hi there..Don´t know if this will help but I built the parallel programmer and Arduino on a breadboard. I wanted to bootload a Mega168 chip. After countless failures I finally suceeded in bootloading the chip as follows....

Downloaded the latest WinAVR
Copied and renamed the ATmegaBOOT_168_diecimila.hex to diecimila.hex and put this file in c:\
Opened windows command prompt
Changed directory to C:\
Then ran the following command...
avrdude -c dapa -p m168 -F -U diecimila.hex

Hey presto...It bootloaded perfectly and is working fine.
The -c dapa instruction uses defaults for anything not specified such as LPT1 as parallel port and -U asumes you want to erase the chip and flash the named file. I put the boot file in root directory and ran the avrdude from root so it automatically looked in that directory for the boot file first.

Hope this helps someone.