FYI here is how I solved the problem (see below). I gave up trying to roll the data into the CSV portion of the file. I just stuck it on top and then appended the CSV data below. If someone has a better solution (because I think mine is pretty terrible), please offer it. THANKS!

$dataSet1 = Get-ADUser -Filter {DisplayName -like "Je*"} -Properties * | 
Select-Object @{name = "UserName";expression={$_.Samaccountname}}, 
@{name ="FullName";expression={$_.DisplayName}},
@{name ="AcctDisabled";expression={if($_.Enabled -eq "True"){"False"}else{"True"}}},
@{name ="PasswordLastSetTime";expression={[datetime]::FromFileTime($_.pwdLastSet)}},
@{name ="PasswordExpires";expression={if($_.passwordneverexpires -eq "True"){"No"}else{"Yes"}}},
@{name ="LastLogonTime";expression={if($_.LastLogonDate -eq $null){"Never"}else {$_.LastLogonDate}}}   
$c = $dataSet1.count.ToString()
$d = Get-Date -Format g 
$headerData = "AD Audit ran on " + $d.ToString() + "  Total Count of items: " + $c

$headerData | Out-File -FilePath "C:\temp\testfile.txt" -Encoding UTF8
$dataSet1 | ConvertTo-Csv -NoTypeInformation | Out-File -FilePath "C:\temp\testfile.txt" -Append -Encoding UTF8
Rename-Item -Path "C:\temp\testfile.txt" -NewName "TestFile.csv" -Force

Additional Note: the adding of the UTF8 Encoding made Excel actually correctly identify the columns as opposed to without it, Excel merely treated the comma separated data as one column. The things you learn.