This isn't entirely true...

If you go into the properties page of the Virtual directory that you are using and select 'High (Isolated)' in the Application dropdown. The Perl for ISAPI DLL will now be started in a separate process (a DCOM server) called dllhost that persists between calls to the server. This process can be killed using task manager and is resurected next time round.

If you have problems getting this to work then you need to add the IWAM_<server> user to your 'users' group. The DCOM server is owned by the IWAM_<server> account. You will need to remember this when accessing network resources etc. with your Perl script.

Your issue with installing CPAN modules is unlikely to be related to the method that you use to execute your script. If you are having problems running your script then permissions are likely to be the problem.