A way to check if you have the module installed is by trying loading module directly and see what happens. For example:
perl -MSpreadsheet::WriteExcel -e1
will be quiet if you have the module installed otherwise it will complain with a message like:
Can't locate Spreadsheet/WriteExcel.pm in @INC (@INC contains: /etc/pe
+rl /usr/local/lib/perl/5.10.0 /usr/local/share/perl/5.10.0 /usr/lib/p
+erl5 /usr/share/perl5 /usr/lib/perl/5.10 /usr/share/perl/5.10 /usr/lo
+cal/lib/site_perl .).
NOTE: The message above includes the current library search locations perl is aware of (in @INC). If the module was installed by standard means (cpan or perl Makefile.pl etc) it should be somewhere in your @INC (library paths) already.