Download and install Nokia Carbide UI
It's a tool Designed to Make theme for Nokia Mobile Phone.
It's Really Easy to Create Theme in it..

Official Description

Carbide.ui

Carbide.ui is now a family of tools for creating themes for Symbian and Series 40 devices.

Carbide.ui Theme Edition 2.0 has been released through the Symbian Foundation. This new version, which supports theme development for Symbian OS, S60 5.0, prepares Carbide.ui to support future Symbian releases.

Carbide.ui Series 40 Theme Edition 3.5 provides enhanced editing support for Series 40 device themes.

Description
The Carbide.ui family of tools enables the creation of themes for Symbian and Series 40 devices. Carbide.ui provides access to the more than 1,000 customizable theme elements in the Symbian UI, which makes the Symbian UI the most customizable UI available. Carbide.ui is designed for professionals and hobbyists alike.