To store the results of the "last" command, just add '> some_file' or '>> some_file' at the end of the command,
where some_file must of course be replaced by the path to and filename of the actual logfile.
The options to be used for the "last" command, you can figure out yourself by reading
For instance, save last 10 logins:
last -10 > /tmp/log_of_10_last_logins
Run this automatically via cron, to update the file at regular times (ie run the command once per day, once per hour, etc).
Use '>>' instead of '>' for appending to the file rather than overwriting the file each time, if you need that.
Your FTP script can then pick up the log (/tmp/log_of_10_last_logins in the example) and put it on your Win 98 computer.