• For installation of most modules, you probably need root access. Perhaps, you could do so with sudo or the like (don't know about).
• Then do try to execute some commands, e.g.:
  

    unless (open (PPM, "ppm install My::Module 2>&1 |")){
      print "Error in executing ppm: $!\n";
    }
    else {
      print "The result was: <HR>\n";
      print <PPM>;
      close (PPM);
    }
  [download]

  or use perl -MCPAN -e "install My::Module" instead of the ppm install - line. But you may get problems if you have to enter something. Maybe you could use the module Expect instead of the simple pipe-open...
• Take care that nobody else can execute this cgi-script (e.g. with .htaccess)

Best regards,
perl -e "s>>*F>e=>y)\*martinF)stronat)=>print,print v8.8.8.32.11.32"