http://www.bitsbox.co.uk/connectors/header_con.html

I have a Chinese knock off, it works as well as an Italian one.  If swapping chips around points to the chip, burning a new bootloader on it tends to sort things.  Its not too difficult is you've got another working Arduino.  Reading the 'ArduinoISP' sketch in the examples in the IDE yields clues or http://arduino.cc/en/Tutorial/ArduinoISP .

Wirewrapping is quick & easy. A good solder joint starts with a good mechanical joint - wirewrap makes that mechanical joint to start, and is quick & easy to change/fix if needed.

Not so quick and easy if you solder it after wirewrapping.    I'd have doubts whether you'd ever get it apart again.......

With a RC circuit its possible to 'emulate' an analog input with a pure digital pin with the 'R' being made by your nail in the soil.. In simple terms you set the pin to output, set it high to charge the capacitor, switch it low and then to input and time how long it takes to discharge to the point where it registers as being a low.  The lower the resistance of what is connected to the pin, the quicker it discharges.  You'd need to use something (multimeter or an analogue pin) to determine an approximation of 'R' the (resistance of your nail through the soil) to determine a suitable value for C.  Plenty of stuff on google to work it out but heres a start : http://www.allaboutcircuits.com/vol_1/chpt_16/4.html.  The digital input will register as low when it reaches approximately 2.5 volts.  This probably appeals more if you're a cheapskate........... 

The default Analog reference is to use VCC which is nominally 5V but in actuality is whatever is coming out of the USB port of the computer.  If you plugged the 3.3V output into the AREF pin of the arduino and told it to use it

Code:

analogReference(EXTERNAL);

It will be reading a voltage relative to whatever is going in the AREF pin (3.3 volts if you connect it to 3.3 Volts).

Lesson one : The chip circled in Red on the Pi is surface mount (a SMD - Surface Mount Device). The chip circled in blue is what used to be standard many years ago - a through hole chip mounted in a socket which is soldered on the reverse side with the legs of the socket going through holes.  They are relatively easy to mess around with a soldering iron and cheaply available stripboard or home made circuit boards. SMD needs specialist gear that a hobbyist isn't likely to have (or even afford).  In a mass production environment, the SMD lends itself to automation and hence cheap to produce in quantity.  

My question is could the arduino wifi sheild transmit real time video to a laptop via a router on a wireless LAN network?

Not a hope in hell, the arduino lacks the required horsepower to process video in real time by several orders of magnitude.  Assuming you're connecting an arduino to said wifi shield of course....

It doesn't matter which you connect the resistor to, it will work on either, the LED still needs it's longer leg (the Anode) to the positive end of the circuit however. 

I have around a dozen Arduinos including thiose I made myself, owning more than one is very useful, especially when it comes to burning bootloaders (google it) and trouble shooting.  One of my dozen is an SMD clone, it has its uses but I can't take the chip off it......

Depends on whether you want to pull the chip out of it or not......

I don't own a Leonardo, but I know they don't do an old school 28 pin chip in an old school 28 pin socket version.  They used to do a SMD (surface mount) version of the arduino Uno, I don't know if its still available.  

If you wanted to take a surface mount chip off a bourd it involves special kit and melting solder.......

The old tutorials should have been updated or removed years ago.  I've been around Arduninos a while, but I never owned one I didn't make myself that didn't have a built in LED on pin 13.

The chip in my home brew is mounted on stripboard, the chip is the same one used in most Deumilanove/Uno/numerous clones. The Leonardoi is surface mount and wouldn't fit, Surface mount is tricky on a small scale hobbyist level. At a push you can program the chip on a Uno, lever it out of the socket and stick in it your own board.  Its just about practicalities.....

The other picture shows it mounted on what I designed it for : mounting on a Raspberry Pi. http://www.raspberrypi.org/faqs

LED's are polarised. They need to be connected the right way round to work.  Plugging one into GND & pin 13 is not a good idea on an arduino made in the last 5 years (including the Uno). There is no current limiting resister in circuit. Its completely unnecessary any way, any arduino made in the last 5 years (The Uno)  will have one on board, already wired and working. Its usually labelled 'L'. The tutorial you've found is out of date and doing it today can damage the Arduino.  You may have already damaged the output on Pin 13.

Home brew Arduino fed directly fed with 5V.



Since the Arduino Leonardo chip is surface mounted it makes the above a bit tricky....



Mounted on a Raspberry Pi

Some nice person did this :   http://blog.markloiseau.com/2012/05/install-arduino-ubuntu/

The troubleshooting section is your likely promlem, ie your user doesn't have rights to access the serial ports.