Hello there i believe the game you are thinking of is Escape Velocity Override, you can download a free trial of it from the companys website
Here . Note that EVO is only compatible with Pre Mac OSX computers no Windows. You can however buy a copy of the sequel Escape Velocity Nova:
Here and then get a plug-in for it that makes it EVO.
Escape Velocity Nova is availible for both Mac OSX Windows and older macs and is one of the best games i have ever played and it is definately worth the money. I understand your emotions in wanting to find this game as i too spent many years of my childhood playing EVO and the original EV