So, you want to program a bootloaded AVR. Or possibly, you have an Arduino Lilypad and no way to program it. There are a few solutions available to you: You could buy a USB to FTDI adapter (available at Adafruit, Sparkfun, etc), you could buy a simple FTDI cable, or you could build something. I couldn't afford the "FTDI Friend," so, I decided to build an adapter to use the TX/RX Serial connection from the Arduino. It plugs in to the RX, TX, Reset, 5V, and GND pins on the Arduino and has a 6 pin female header for the FTDI connection. This can most likely be made with electronics supplies you already have.
Step 1: Materials
Not much is needed at all for this. The only materials you need are:
-6 Pin Female Header
-6 Male Header Pins, broken into sections of 4 and 2
And the only tools you need are:
-Hemostats help a lot with holding the wire in place
-Fine Tip Permanent Marker
Step 2: Soldering: Part I
Solder your 5 cables to the header. I used red cables for the data and white for everything else. On the leftmost (or rightmost if you're turned the other way) side, connect the ground wire to both of the terminals on the end. Once you're done, wrap in electric tape and label it with the marker. Make sure to keep the cables aligned.