Check the BloodBath HowTo for Blood multiplayer with DOSBox:
viewtopic.php?f=12&t=1149
Depending on the connection between you and the other player, this might prove to be a bit laggy, however.
Alternatively, if you are very tech-savvy, you can try the following DOSBox version:
http://home.arcor.de/h-a-l-9000/
You will want to check the section "NE2000 passthrough patch for DOSBox".
It has a NE2000 pass-through, which means it will be more efficient than the native DOSBox solution (ipxnet).
The problem with that is that you will have to set up a VPN so that you're on the same subnet as all the other players. You can then configure DOSBox to use the network interface of the VPN.
I have tested the latter method successfully with some other IPX-based DOS games, so Blood should also work.