I can't remember where I heard this, but I think someone told me that you can't download custom levels over a local network.

• Have you tried hosting with a regular level?
• Have you tried putting the custom level on your brother's computer?
• Have you tried connecting to the server through "Internet Play"?
• If so, have you tried connecting by choosing it on the server list?
• Or have you tried (on your brother's computer) entering, in the "Address" space at the bottom of the server list, the internal IP address of your computer (hosting JJ2 server)?
• Have you tried connecting through "Local Network TCP"?
• You say your brother can't access the house network. What are the details of this?
• Can he not see shares on the other computers?
• Is there nothing in "Network Neighborhood"?
• Can other computers see him in network neighborhood?
• Can he access the internet?
• Normally, to see other computers in the network, you have to be logged in at the Windows Network Logon. Could this be why he can't access the network? Does he just press ESC or click Cancel at the login dialog?
• Does he have a software firewall on his computer?
• Do any of the computers have a software firewall?
• How many computers are on the network?

More information please