Are the 2 boxes connected through wired or wireless connections to the router?
Can the OpenBSD box ping the Windows7 box? And vice-versa?
For ftp you not only need port 21 open but also the following port range
Code:
$ sysctl -a | grep porthi
net.inet.ip.porthifirst=49152
net.inet.ip.porthilast=65535
Port 21 is used for the ftp commands. The actual transfer is done with ports choosen randomly from the 49152-65535 range. At least for passive ftp