With the squats its just body weight.

The thing with tabatas is its just maximum effort for 20 seconds, even if it means your only just jogging, which I imagine ill be doing on the 8 th set the first time I reach it

Theres no bettering distance or time involved, just as hard as you can for 20 seconds.

As for timing them, there is a little stopwatch gadget you can get for about 15 quid off ebay called a gymboss. I think it was actually made for tabata training.