So I wanted the full display name so I have updated your script.
$dom = $env:userdomain
$getusr = quser | Select-Object -skip 1
$usr = $getusr.substring(1,22).Trim() -join ","
$display = ([adsi]"WinNT://$dom/$usr,user").fullname
Set-ItemProperty -Path "HKLM:\Software\MMSOFT Design\PC Monitor\" -Name ComputerName -Value "$env:computername - $display"