[astroglide]

ah, missed the 'wired on the other side' requirement.

my inclination would be to simply broadcast wireless from apartment A, and have a wireless adapter on the ftp server (presumably this is 24/7) in apartment B. the ftp server can share the connection through a physical ethernet adapter. ap-to-ap and ap-to-wireless bridge (plugged into a standard switch on the other side) both sound like they're begging for reliability problems with encryption enabled, and you should be using wpa/tkip at a minimum.

in this situation, your only requirement is to have one system maintain a persistent connection to one access point - a lot simpler and easier to debug than multiple aps. the 'downside' is that it should be up 24/7, but that's sort of a given for a server and fairly standard for regularly used pcs. the internet connection sharing in xp has proven stable to me, so that aspect shouldn't be a concern if you're not running a server os. if none of the other systems need port forwarding it should work fine, and if you have a decent signal over there you don't need any additional hardware to try it out right now.