I think that Win32::Process is included in Activestate Perl 5.8, although I'm not sure. Try this:

perl -MWin32::Process -e 1
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If you don't get any errors, you're good to go. This error

'cl' is not recognized as an internal or external command,
operable program or batch file.
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means that you don't have a C compiler installed. When you install modules that have ".xs" components, you need a C compiler. Specifically, you need to use the same C compiler that was used to compile the particular 'perl' program you are using, in this case Microsoft Visual C++. The good news is that you can use the Standard or even, I think, the Learning Edition to compile XS modules. It's not too expensive.