Well first off making a theme is not something you can do over nite. You need to have a some sort of graphic editor (photoshop,gimp,etc.).
You also need resource program like reshack or restorator. Along with a copy Ave's Windows7 Style Builder this is the app that the artist here used to change all the styles with. once you have that their are numerous tuts in this section [Only registered and activated users can see links. ] I would suggest starting with dave senior complete guide [Only registered and activated users can see links. ]