I\'m running PowerShell in a Windows 7 x64 virtual machine. I have a shared folder on the host mapped as a network drive (Z:). When I run PS normally I can access that drive
How about mapping a new psdrive to acess that data? PSDrives work just as well if not better than system mapped drives when you are writing scripts or accessing network data stores in powershell.
Instructions for using the New-PSDrive cmdlet are here: Technet:New-PSDrive
If you don't want to have to make a new psdrive every time you could add it to the profiles for both the Administrator and your user account and it will automatically be available every time you open powershell.
~Dan