The path to the Program Files directory can be found in the registry at
HKLM\Software\Microsoft\Windows\CurrentVersion\ProgramFilesDir

The drive in which the script resides can be found using

use File::Spec::Function qw( rel2abs );
my ($drive) = rel2abs($0) =~ /^([A-Z]):/i;
[download]

Note that this won't work if the script was launched using a UNC path. ($drive will be undef.)