[NSThread detachNewThreadSelector]

detachNewThreadSelector.m

- (IBAction)clickButton 
{
   [NSThread detachNewThreadSelector:@selector(startBackgroundJob) 
                            toTarget:self 
                          withObject:nil];
}

- (void)startBackgroundJob 
{  
   [self performSelectorOnMainThread:@selector(makeProgressBarMoving)
                          withObject:nil
                       waitUntilDone:NO];
}

- (void)makeProgressBarMoving
{
   NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; 
   float actual = [progressBar progress];
   if (actual < 1)
   {  
      progressBar.progress += 0.01;
      [NSTimer scheduledTimerWithTimeInterval:0.5
                                     selector:@selector(makeProgressBarMoving)
                                     userInfo:nil
                                      repeats:NO];
   }  
   [pool release];
}