For vice versa you have to look at tinysmb.
-which was mentioned first in this thread.

http://my-maemo.com/software/applica...to=1853&faq=37

For the ip of the winpc you have to open a doswindow and execute IPCONFIG , that will tell the ips of all the interfaces.

However, if all you want to do is to synchronize files between them, then you can do like i do by using RSYNC on the N900 to a folder on the shared drive.
(GRSYNC will install rsync and provides a easy to use graphical frontend for it)