Here's another Win32 specific method using windows scripting FileSystemObject:

use warnings;
use strict;
use Win32::OLE;

my $fso = Win32::OLE->CreateObject('Scripting.FileSystemObject');
my $drive = $fso->GetDrive('C:');
my $free = $drive->{FreeSpace};
my $size = $drive->{TotalSize};

printf "disk size = %d MB\n", $size/(1024*1024);
printf "disk free = %d MB\n", $free/(1024*1024);
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