Well I use IRT and here is a useful guide to Backtesting http://www.linnsoft.com/tutorials/F_trader_backtest.htm
In defense of Metastock: I actually find Metastock being somewhat limited as an advantage. If you system test over a long (as in 15 years or longer) period of time, most of your successful systems will tend to be on the less complex side, unless you want to curve fit. Except if you day trade, thats another story. Just my humble opinion.