There are just 3 simple steps to install your SharePoint theme. Please make sure to replace all variations of ‘THEMENAME’ to the name of the theme you have purchased. For example, if you purchased Cedar Blue you would replace ‘THEMENAME’ with ‘CEDARBLUE’ etc.
Step One
Copy the THEMENAME folder into:
Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\THEMES\
Step Two
Copy themename-thumb.png into:
Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\TEMPLATE\IMAGES
Step Three
Open the SPThemes.xml file, located in:
Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\LAYOUTS\1033\
Copy and paste the below code into the file:
<Templates><TemplateID>THEMENAME</TemplateID><DisplayName>Theme Name</DisplayName><Description>SP Themes: Theme Name</Description><Thumbnail>/images/themename-thumb.png</Thumbnail><Preview>/images/themename-thumb.png</Preview></Templates>
Your theme should now be available to apply to your site!