On the windows pc I use winscp and on my n800 i install openssh.

http://winscp.net/eng/index.php
http://www.gronmayer.com/it/index.php

winscp is a two paned explorer type interface for the PC which allows me to securely ftp (via ip address) to the Nokia N800 and transfer files in either direction over wi-fi securely. (sync files etc)

tip. only install main openssh program on N800 where you will be asked to change password for root if you have not already done so. openshh for NIT's can be found in the maemo extras repository, if you do not have repo already installed in application manager