You need to force the second hash to be evaluated in a hash context. That means enclosing it in %{...} (those are braces, not parens).

my %prochash;
# sub call to populate hash
for (my $i = 0; $i < $prochash{NumProcessors}; $i++)
{
 foreach (keys %{$prochash{'Processor$i'}})
 {
   print "$_ : ",$prochash{"Processor$i"}->{$_},"\n";
 }
}
[download]

Cheers,
Ovid

Update: Oy! That's what I get for dashing off a quick answer prior to running to work. I did not say "hash context". I wouldn't say anything like that. Would I? :( Sigh... time to inject more coffee.