[CmdletBinding()]
Param
(
[Parameter(Mandatory=$true,Position=1)]
$Source = "C:\Downloads",
[Parameter(Mandatory=$true)]
$Dest   = "\\myserver\c$\myfolder",
[Parameter(Mandatory=$true)]
$DriveLetter = "J",
[Parameter(Mandatory=$true)]
$Username = "administrator",
[Parameter(Mandatory=$true)]
$Password = "Complex_Passw0rd"
)

$SecurePassword = ConvertTo-SecureString $Password -AsPlainText -Force
$mycreds = New-Object System.Management.Automation.PSCredential($Username, $SecurePassword)

Write-Host "Mapping the Drive Letter in PowerShell"
New-PSDrive -Name $DriveLetter -PSProvider FileSystem -Root $Dest -Credential $mycreds

Write-Host "Copying the files over to the remotely mapped drive letter"
Copy-Item -Path $Source -Destination $DriveLetter -Recurse