So I followed this guide (as well as scavenged through the rest of BI's forums and armaholic's forums) and I STILL can get my P drive to mount..
Here's a link to a video of me running through the process.. It matches exactly how hoverguy had posted it.
https://youtu.be/86pnreyZOgs
I also took a snap shot of what the cmd window looked like when it tried to install the P drive in the video.
http://imgur.com/D3oWHtp
I'd love it if someone could help me trouble shoot why I'm not able to mount the P drive!
EDIT: I just fixed the issue: the Steam.exe must also not be running as administrator.
Hoverguy, I would recommend you add this to your tutorial as many arma players may have this option selected in the properties menu. I was instructed to do so due to the number of mods I use.