backup the mail folder. Just in case, backup the registry key HKEY_CURRENT_USER\Software\RIT\ too.
Install theBat on Win7 PC, and copy the mail folder to it. Then with Regedit go to
HKEY_CURRENT_USER\Software\RIT\The Bat!\
and modify Working Directory to match the path to the mail folder. Then start theBat and it display accounts etc.
In fact you do not need to install theBat, but can just copy the install folder, mail folder and import the registry key to the new PC.