Well consider this:
Lets say you can test 100 trades, and want to do 99% confidence. This would mean your margin of error is about 13%. To reject the null hypothesis, you would need to have 61/100 profitable trades. But there is a stochastic element to the market, and the backtest is only accurate to 61 +/- 13 trades, 1 Sigma. A one standard deviation error is not an unlikely event... It is reasonably likely that your 61% win rate is actually a 48% win rate.
With only 100 trades, you really can't reject the null hypothesis reliably. Even with 666 trades, it is difficult.
If you want to trade systematically, I would recommend shelling out a bit of cash for decent historical database. Otherwise, your backtests will not be statistically significant, when margin of error is factored in.