If you want to create a visual style for Windows XP, you can use StyleBuilder software. This software is published by TGT Soft which unfortunately has closed down that's why StyleBuilder is no longer updated and has many bugs.
Nevertheless you can still download a trial version of StyleBuilder for 30 days at the following address: http://www.clubic.com/telecharger-fiche10606-stylebuilder.html
If you want to create a visual style for Windows Vista or Windows 7, you can use Vista Style Builder software. Sold for 16,50€ (22.50$), this software is updated regularly and has a great community that will be able to help you.
Information : Vista Style Builder and Win 7 Style Builder are one and the same software. If you install the software on Windows Vista, it will allow you to create a visual style compatible with Windows Vista. If you install it on Windows 7, it will allow you to create a visual style compatible with Windows 7.