Ah - a windows user!
Just curious - Why would you need to open more instances on a Mac? A lot of apps allow opening a new window, such as browsers or many word processors. Some will allow large numbers of open docs or browsers (as long as you have a reasonable amount of memory, and a fast processor) You don't have to worry so much about an app crashing, (at least it's not MS Windows...)
edit < I see you have a lot of posts regarding software development - I can see good reasons for needing to open more than one instance for those purposes. If my comments were somewhat sarcastic, that was not really my intent. >