If I'm not mistaken, you want to require instead of use in your eval block.   Here's how I did similarly a while back:

my $have_SWE;
BEGIN {
  $have_SWE = 0;
  eval { require Spreadsheet::WriteExcel };
  unless ($@) {
     Spreadsheet::WriteExcel->import();
     $have_SWE = 1;
  }
}
if ($have_SWE == 1) { ... }
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If memory serves, I picked that up from something merlyn once said or posted.
    cheers,
    Don
    striving toward Perl Adept
    (it's pronounced "why-bick")

Update:
Super Search for "module installed" is what lead me to this thread, where I learnt of BEGIN, eval, and require.

Update:
After discussing with brother BUU, the lone advantage I can see of BEGIN... eval is that it allows you to include a more user-friendly message in the event that Tk isn't installed.   As always, Wiser Monks Than I may very well rightly say that I'm fullabeans.   {grin}

Untested, but perhaps a wee bit cleaner than my original code example:

my $have_Tk;
BEGIN {
  $have_Tk = 0;
  eval { require Tk };
  $have_Tk = 1 unless ($@);
}
if ($have_Tk == 1) { ... }
[download]