In this (http://media.fxguide.com/fxguidetv/fxguidetv-ep087.mov, scroll to half way) video Hakan Andersson talks about mental mill, si has support MetaSL shaders, but this ability was blocked in final release, how can unblock this feature, something like xsi_unsupported_metasl=1 , where is that?

much later edit (to avoid unnecessary confusion):
The correct procedure you'd have to follow is outlined
in the blog entry Stephen Blair references two posts down...

Thank you, Hirazi! I will surely test it soon..

Can the re-registering of the mentalray.dll you mention in your blog
also be done within the setenv.bat?
Or is it a one-time operation?

It's a one-time thing.
Unless you unset the env var, In that case, I think you might have to reg the dll again when you re-set the env var.

PS runonce uses cmdreg.

Thanks for the info

MetaSL has never been tested. We don't know if it works, if the scenes save correct, etc,
so use at your own risk