if you have a service agreement, the serial number of the program and have created an account at MyIpswitch at https://www.myipswitch.com/licensing/index.aspx , then you can redownload the software from there.
if you have your WS FTP Home configured for your sites with user name and password you need to find the ws_ftp.ini file that stores the information on your Vista OS and back that up, then install it in the appropriate spot in the new Window 7...
you maybe interested in this article...
http://ipswitchft.custhelp.com/app/answers/detail/a_id/595/kw/ws_ftp.ini%20vista/r_id/166