Update @ 2013-08-10: It is found that there is no way to register the installed Windows XP. I tried to use the KEY file in the archive inside sources\xpm but that is not valid. It seems that we have to use the Windows Virtual PC. For more info, please refer to the following post.
XP Mode Unauthorized Key
It’s really funny to see how a BIG corporation like MTR recruits employees. The candidate needs to complete a few online tests. And these tests have to been done in a Windows XP machine and only support Internet Explorer. This is how things work in Hong Kong~~
Anyway, i solved the problem by setting up a Windows XP virtual machine by following the article written by Melanie Pinola.
How to Run Windows XP for Free in Windows 8