Even the basic map pack they run won't allow him to connect on his machine. The strange thing is that he can goto other CTF servers and play on the same (non-custom) maps they have in Vile/Brutal CTF. I did have him turn Automatic downloading on but it will either do two things:
1) The download won't start or
2) come up with a downloading error
This is on a Windows Vista O.S. I dunno if there could a firewall issue or a setting that needs to be done on his side to get him connected.
I don't think it's a Windows Vista issue if he can connect to other servers and the downloads works from there.
Make sure that you have the required maps, or the standard OA ones, in the right location before connecting. You can also try and delete the q3config.cfg in case if the cl_allowdownload variable is being overwritten. Apart from that, do you get an error message indicating something with libcurl or similar before the download breaks? (check in the console and note whatever message it types).