No it's not you at all. I have made a patch for ExtUtils::Installed that will allow you to supply a list of locations which are outside the perl install prefix - I need to add some tests and change the documentation before I send it to p5p but this:

--- Installed.pm.orig   2004-07-20 16:37:50.000000000 +0100
+++ Installed.pm        2004-07-20 17:23:53.000000000 +0100
@@ -77,24 +77,32 @@
 }
  
 sub new {
-    my ($class) = @_;
+    my ($class, @dirs) = @_;
     $class = ref($class) || $class;
     my $self = {};
  
-    my $archlib = $Config{archlibexp};
-    my $sitearch = $Config{sitearchexp};
+    push @dirs, $Config{sitearchexp}, $Config{archlibexp};
  
     # File::Find does not know how to deal with VMS filepaths.
-    if( $Is_VMS ) {
-        $archlib  = VMS::Filespec::unixify($archlib);
-        $sitearch = VMS::Filespec::unixify($sitearch);
-    }
  
-    if ($DOSISH) {
-        $archlib =~ s|\\|/|g;
-        $sitearch =~ s|\\|/|g;
+    foreach ( @dirs ) {
+       if (!m!$Config{archname}/?$!) {
+              $_ = File::Spec->catfile($_, $Config{archname});
+       }
+
+       if( $Is_VMS ) {
+           $_  = VMS::Filespec::unixify($_);
+       }
+
+       if ($DOSISH) {
+           s|\\|/|g;
+       }
+
     }
  
+    my $archlib = @dirs[-1];
+
+
     # Read the core packlist
     $self->{Perl}{packlist} =
       ExtUtils::Packlist->new( File::Spec->catfile($archlib, '.packli
+st') );
@@ -108,11 +116,15 @@
         # Hack of the leading bits of the paths & convert to a module
+ name
         my $module = $File::Find::name;
  
-        $module =~ s!\Q$archlib\E/?auto/(.*)/.packlist!$1!s  or
-        $module =~ s!\Q$sitearch\E/?auto/(.*)/.packlist!$1!s;
+
+        foreach my $dir ( @dirs ) {
+           $module =~ s!\Q$dir\E/?auto/(.*)/.packlist!$1!s and last;
+        }
+
         my $modfile = "$module.pm";
         $module =~ s!/!::!g;
  
+       print $module,"\n";
         # Find the top-level module file in @INC
         $self->{$module}{version} = '';
         foreach my $dir (@INC) {
@@ -131,8 +143,8 @@
           ExtUtils::Packlist->new($File::Find::name);
     };
  
-    my(@dirs) = grep { -e } ($archlib, $sitearch);
-    find($sub, @dirs) if @dirs;
+    my(@search_dirs) = grep { -e } (@dirs);
+    find($sub, @search_dirs) if @search_dirs;
  
     return(bless($self, $class));
 }
[download]

use ExtUtils::Installed;
                                                                      
+          
                                                                      
+          
use lib qw( /home/jonathan/foo/lib/perl5/site_perl/5.8.1);
                                                                      
+          
my $ff = ExtUtils::Installed->new('/home/jonathan/foo/lib/perl5/site_p
+erl/5.8.1');
                                                                      
+          
print $ff->files('Foo','all');
[download]

/J\