using pasteboard ( NSString )

NSPasteboard *pBoard = [NSPasteboard generalPasteboard];

// get
NSString *szStr = [pBoard stringForType:NSStringPboardType];

// set
[pBoard setString szStr forType:NSStringPboardType];

[ 참조 ]
http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/ApplicationKit/Classes/NSPasteboard_Class/Reference/Reference.html