Mkaing your own theme?

So everybody here knows that Windows XP uses .theme files for its appearance settings. Its UI comes from the large Luna theme file stored somewhere in your Windows directory. Now what I want to know is that, is it possible for me to open the Luna theme and modify or add parts to it to my own liking. I mean the Windows themes just suck, and using those Theme programs is such a hassle for me. I just want to modify somethings like add a new colour to the taskbar and start menu and such. Is it possible to do so, and if so how?

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Microsoft = Catholiscism-Mainstream!
Mac OS X = Orthodoxy-Secluded!
Linux = Protestant Denominations-No standard!
Conclusion: Religion has no place in computers!