Lego-Mindstorms and Dolphin, which robot kit to buy?

> I'd like to create some Dolphin controlled robots.
>
> The Bot-Kit software on the ObjectArts site is for Dolphin version 2.1
> I'm not sure which version if the LEGO Mindstorms is supported.
>
> So,
>
>     Which MindStorms set should I buy?
>         Robotics Invention System 1.5?  2.0 out?
>
>     Does anynone have an upgraded version of the Dolphin Bot-Kit, for
>         Dolphin 4.0 or 3.0? Or does the existing 2.1 kit work OK?
>
> Thanks,
> Richard
>
> PS Any buying tips for the Netherlands are welcome.