perl -MCPAN -e shell / ppm / vpm - do what exactly?

[Oliver Glass]

I have activestate perl installed on NT and used to use VPM for
installing packages. Recently, I discovered 'perl -MCPAN -e shell' when
using cygwin and found it works on NT also. I know ppm is something to
do with packages too...

So what's the difference between these three?

        perl -MCPAN -e shell
        ppm
        vpm 

Are there any other package installers out there? Do these utils offer
any more functions than installing packages?

Thanks,

a curious beginner,

Oliver