Attached Link: Add a script to Python Panel

 I'm just learning about this myself, but here's what I know (I'm using Poser Pro, by the way, but I think it's the same process for Poser 6 and 7. I don't know about Poser 4 or 5):

1. As you said, drag and drop the py file to the appropriate Python folder. (What that folder is may depend on how you want to access the script. See the attached link to some very clearly described options about that.)

2. The simplest way I know to open the Python script and is

a) Open a Poser scene
b) Click on File>Run Python Script
c) A browser opens. Browse to the location of the desired py file, select it, click on "Open"

When I do the above, the Python script opens. 

I'm counting on others to make any necessary corrections/alterations to the above!

Hope this helps.