Theme requirments ?

Can someone tell me why some themes have 5 files ( .theme , .msstyles , .msstyles.mui , shellstyle.dll.mui , and shellstyle.dll ) and others have only two ( .theme & .msstyles ) ? Thanks for any help.

the ones with 5 files u are created a whole new theme set while the one with 2 u are replacing files in the pre existing aero folder

THANKS for the info. Undine