For me, every time I try to install it, it wants to default to C:\Users\Myname\Desktop\SimCity 4\Plugins\Network Addon Mod.
I cannot for the life of me figure out why it wants to install to the Desktop. SimCity Deluxe is installed into C:\Program Files (x86)\Maxis\SimCity 4 Deluxe, my documents is on another physical drive at D:\Documents where there is no SimCity folder (as I didn't go past the NAM installer, and have no other plugins).