I have an app which, when buttons are pushed loads sheets, each of which have their own nib file. I made instances of the classes in IB and hooked the buttons up to the appropriate actions. I don't know if this is the best way to do it, but it works. This is an example of how I did it with Java:
public void openSheet(NSButton aButton) { //this action was hooked up in IB
NSApplication.loadNibNamed("theSheet", this); //this loads the nib file
makeSheetAppear(); //this is the method that actually makes the sheet appear
}
public void makeSheetAppear() {
NSWindow theWindow = NSApplication.sharedApplication().keyWindow();
NSApplication.sharedApplication().beginSheet(sheet Window,theWindow,null,null,null);
}
Hope that helps.