How to use New-Object PSObject

$(Foreach ($mailbox in Get-Recipient -ResultSize unlimited -RecipientType UserMailbox) {
    $stat = $mailbox | Get-MailboxStatistics | Select TotalItemSize
    New-Object PSObject @{
        FirstName = $mailbox.FirstName
        LastName = $mailbox.LastName
        DisplayName = $mailbox.DisplayName
        TotalItemSize = ($stat.TotalItemSize/1.0GB)
        PrimarySmtpAddress = $mailbox.PrimarySmtpAddress
        Alias = $mailbox.Alias
        }
}) | Select FirstName,LastName,DisplayName,TotalItemSize,PrimarySmtpAddress,Alias |
Export-CSV C:\MailboxReport.csv -NoTypeInformation

The above code is returning:

FirstName,LastName,DisplayName,TotalItemSize,PrimarySmtpAddress,Alias
,,,,,
,,,,,
,,,,,
,,,,,
,,,,,
,,,,,
,,,,,
,,,,,
,,,,,

Do I need something like this:

 $object = New-Object PSObject
      Add-Member -InputObject $object ...

I'm trying to compile a report with data gathered from Exchange 2007 on Server 2003 x64 using PowerShell 1.0.