You do not need to use drive letters to access information provided by PowerShell providers. For example, you should use this to list the HKEY_CLASSES_ROOT you have in your registry:
Dir Registry::HKEY_CLASSES_ROOT
By pre-pending the path with the provider name that PowerShell should use, you no longer need drive letters. Or, you could add new drive letters to locations not covered by existing drive letters:
New-PSDrive HKCR Registry Registry::HKEY_CLASSES_ROOT
Dir HKCR:
Dir HKCR:
