[R-pkg-devel] Package requiring cmake; windows only package dependency?

Hi,

I am currently preparing a package for hdf5 that ships and compiles from
source on windows. The intention here is to avoid having to ship or
download a binary from an unknown source. As a dependency, I need the cmake
program installed.

Here my question:
1. Is cmake installed on win-builder? If not, could it be installed? If
yes, in a specified standard location or available through the PATH
variable?
2. How do I specify that a package is only intended for a specific OS?

On another note here:
The package I am preparing would only compile the binaries on windows. On
other systems, I would prefer to have people install them thought native
services (e.g. apt-get) to make configuration etc. more manageable for
system administrators (even though that puts a little more burden on the
end-user on these systems).

Second question:
Is there a way to specify an OS-specific dependency? As the hdf5lib package
is rather large and intended for windows only, I would prefer if it isn't
downloaded anywhere else.

thanks for your help

Holger