Thank you very much. That clears a lot of things. 
It still seems like you are using one serial port on the Uno to talk to two devices - the XBee and the PC. That won't work.
I have been told that such thing won't work before. The reason that I attempted it is that one of my friends mentioned to me at one point that it works and it is some sort of hardware serial hack. To be honest, it seems to be working not taking into account the delays. However, do you think that the reason behind the delays is using the same serial port for two things and also would you be able to tell me (or refer me to some article or website) the reason why such thing shouldn't work based on certain principles?
All that said, I really appreciate that you have been patiently following up this post. 