I think there is a very hard way or expensive to convert it (if it available in anyway !)
I developing a themes using NetBeans , its make thing easy and fast , just install it and install portalpack plugins to it , and then you can develop a new themes, hooks, portlets and etc. !
NetBeans :
http://netbeans.org/downloads/index.htmlPortalPack :
http://contrib.netbeans.org/portalpack/If you have images, JS, CSS files of your Drupal theme, I think its will be good to develop it , I think its not so easy and not so hard too to learn how you develop a new theme for liferay ...
If you want to know how you Integrate a Liferay with Netbeans and Install plugins and then how to start I will explain it ( Inshaa' Allah )
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