Note: the link
bassfisher6522 gave is for just the absolute
basics of making a theme, if you want an entirely new theme like those seen when people edit their theme dll's. Then you'll have to find a resource editor to edit your
explorer.exe, the
aero msstyles file in your Windows\Resources directory, and your
explorerframe.dll
Explorer.exe - Contains data for your start orb mainly that people like to edit
Explorerframe.dll - Contains data for your Explorer view navigational buttons mainly
AeroMsstyles - Contains data for your entire Windows aero and basic styles images
That's what i've done, but make sure that you have backups of your originals, or you know well how to use System File Checker to revert back to originals.
Or something like
Code:
sfc /scanfile="C:\Windows....file.ext"