How does the OS determine the priority for icon/application assignment

FROM : Development
DATE : Wed Jan 30 23:23:26 2008

One of the programs I've written isn't having it's icon as the default 
the for the file types it handles. Basically the Icon and default 
application are for another application and not my own, even though 
the application they are for has been removed from my system and my 
application run several times. Is there some setting I need to make 
that causes the OS to recognize my application as the default?
I did manage to get my icons and such to be the default at one point, 
but the instant I installed the other application on the computer the 
icons all switched... What I am wondering is what this application is 
doing that forced the change? I thought it might be alphabetical by if 
that were true my application would be default.


Thanks for any help.