Hlm probably has the best advice so far as you are most likely trying out different platforms after initially trying Tradestation (TS). These two threads talked about Infinity and OEC:
http://www.traderslaboratory.com/for...ysis-3163.html
http://www.traderslaboratory.com/for...or-e-3725.html
One platform that could take data from TS and do trade simulations is Ninjatrader (NT), and that is certainly a free for simulation platform that you should try out. Their DOM is competent enough and feature rich enough and their simulator is probably as good as any out there (IMHO, it is better than the newly released TS simulator because you could quickly switch from simulation to live and you could replay any recorded data for further practice and analysis). Beware that actual live trading with NT is not free and there is no way to trade with TS- RJOBrien as the broker because TS does not allow an open API to route the live orders using a third party software such as Ninjatrader.
What you will learn from NT is not all for loss because there are many other brokers that will take live trade signals from NT.