1) Customization Tools
65 Series Customization Tools package contains the Colour Skin Editor and the Theme Editor. Both of these tools will help interface designers develop top of the line themes for Siemens 65-series phones.
That is all you need if you wish to make the theme. The following tools will be needed if you want to preview the themes on your computer.
2) SMTK Core Pack
It is a set of emulators, control and integration utilities and preverifiers for Java™ and Series 60 development.
3) Depending on which phones you're theming for, you'll need it's emulator packs. There's 2 ATM: 45 & 55 Platform Emulator Packs & 65 Platform Emulator Packs
Bad news: that sums up to 60 mb + (if inc. emulator)
Good news: the emulator is cool. You can even play java games on it!