If it's an application that you can access with OLE, you could use something like this (which I use to either use an open instance of excel or create a new one..

    my $exl = Win32::OLE->GetActiveObject('Excel.Application') || 
     Win32::OLE->new('Excel.Application');
[download]

There's also some API call's.. but I've never used them with Perl. Here's the link to some VB code that will do what you're looking for. Now, you just have to figure out how to use that and Win32::API

Hope this helps..
Rich

Whoops.. this was supposed to be a reply to the question.. not the first answer :)