Currently, there is probably a bigger market for blog themes such as for the WordPress content management system but that will require some PHP knowledge.
There is basically three business models used by template designers: 1. Sell a template for a fixed fee, 2. Sell a template as an annual subscription with gives buyers access to support and updates and 3. Give the template away for free on a website filled with advertising. As this market is quite saturated if your skills is not exceptional then giving away the template for free and depending on ad revenue is not a bad idea.
If you are selling a template for a fixed fee you can use a marketplace such as Theme Forest to sell to people but they will take a commission of every sale.
Some local guys who have built large businesses from selling website templates are WooThemes and Obox Themes.