Streight from the helpfile:
Returns the name of the Nth open dcc chat window.
Properties: ip, status, cd
$fserv(0) returns the total number of open fserves
$fserv(1) returns the nickname of the 1st fserve
$fserv(1).cd returns the current directory of the 1st fserve
If you specify a nick and N, it will return info on the Nth window for that nick.