Yeah g'day,

Our generous Bhagwan recently provided details of a site which should assist you greatly:
http://www.ozracetools.com
In answer to your specific query the correct method to follow is to add 1 to the odds of each runner and then inverse bets on each runner:
eg. 2/1 + 1 = 3
3/1 +1 = 4
then inverse bets, ie4 units on the 2/1 runner(return 12 units),
3 units on the 3/1 runner( " 12 units),
so whichever runner wins you collect 12 units for an outlay of 7 units.

Cheers.