In both snippets, right before opendir, print $path. You'll notice they're different.

"c:/documents\ and\ settings/username/desktop/perf_analyzer"
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is the same thing as

"c:/documents and settings/username/desktop/perf_analyzer"
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Both of the above produce the string

c:/documents and settings/username/desktop/perf_analyzer
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Expressions that produce the string

c:\documents and settings\username\desktop\perf_analyzer
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would also be fine. Your bug is

$path=~s/\s{1}/\\ /g;
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You are causing the string to become

c:/documents\ and\ settings/username/desktop/perf_analyzer
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That's bad, because there's no directory c:\documents

Fixed code:

chomp( my $path = `cd` );
opendir MYDIR, $path
   or die("Can't open dir $path: $!\n");
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Even better:

opendir MYDIR, '.'
   or die("Can't open current dir: $!\n");
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