I normally live in East Africa in an area where you can't buy yogurt so all of us 'Wazungu' (white people) have figured out a very easy way to make yogurt from powdered milk. This is by far the easiest way to make yogurt I have seen because you never have to worry about getting the temperature right. It's perfect for a beginner and for busy mums. It takes about as long as it takes for your kettle to boil. I make 2 litres at once and here it is:

Put the following ingredients IN ORDER in a container with a lid:
2 cups room temp. water
4 cups just-boiled water
3-3.5 cups milk powder (we only have full cream powder available so haven't tried skim)
4 Tbsp natural yogurt (the fresher the better)
2 cups room temp. water

Stir and cover. Wrap a couple towels around container and leave out for 4-12 hours, then refrigerate.

Stir and remove 1 or more 4 Tbsp. servings and put in freezer for next batch. You don't need to defrost but if you prefer to defrost, do it overnight in the fridge and not the microwave to reduce risk of killing the yogurt.

TIPS:
1. The longer you leave it out to incubate, the stronger the flavour will be.
2. By varying the amount of milk powder you put in, you can obtain your preferred thickness. I find 3.5 cups to be closest to the thickness they sell in Australia whereas 3 cups is thinner like in Europe.
3. If you live in a cold place, you may need to use a more insulated container.

Enjoy!