[kami]

Sorry for the stupid question ...
While running Win7 on 64bit, Maxwell2 on 64bit and Rhino4 (still 32bit)
Do I need the 32bit or 64bit version of the plugin?

[JDHill]

Install the plugin that matches the architecture of the Rhino you will be using it in. So, on x86 operating systems, you will only ever use the x86 plugin, while on x64 systems, you may use one or both, depending on whether you're running Rhino 4 (always x86) and Rhino 5 x64 concurrently.

In your case, install both the x86 and x64 plugins.