Plugga,
As for all betting you need to find the overlays to make a consistant profit. So in theory you should:
1. Work out the winning chances for each horse that has a "reasonable" chance of winning.
2. Work out the quinella odds for each combination of any two horses you identified in Step 1.
3. Bet on any combinations where the available odds are better than the calculated odds (allowing a reasonable margin for errors and profit!)

As I said this is just my theory - at the moment I am just collected quinella data from the NSW TAB site for each race so that I can test this against a reasonable amount of data.

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"Computers can do that????" - Homer Simpson