TL;DR : 
Chat Application Used -> finding msimn.exe process
Last time the application was used -> userassist plugin and look for the binary
How many unread messages -> Registry HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\UnreadMail<email address>
Version -> Registry HKEY_CURRENT_USER\Software\Microsoft\Outlook Express\5.0\Shared Settings\Setup