Tom Phoenix (one of the authors of the Llama book along with our own merlyn) has a program called Inside available here that does this.
Here is a blurb from the readme:

This program will try to report which Perl modules are available
on your machine, along with some other useful information.
Although it's especially made to be helpful to CGI programmers,
it may be of use to other Perl users as well.
 
Note that I've done more than a few weird things in this code in
order to make it work in some odd surroundings. The right thing
to do in general is to fix the broken environments, rather than
to work around them. But since the purpose of this program is to
diagnose some of those broken environments, I'm breaking the
rules. In short: Don't Do As This Code Does! Use the accepted
techniques, instead.
[download]

I found it useful and pretty easy to run and will give you far more information than you (or at least I) need.

requisite obfuscation sig below:
perl -e 's;;uoli;;$a=length;y;g-w;e-u;;;$a--;s;j;$a;;print"$_\n";'