You really need an isa card? Would it work using ne2k_pci?
Sadly, I don't think so.
The packet driver sets the io area at 0x300. If I try a PCI card with a PCI packet driver (e.g. the Intel E1000) then there is no way to set the io area. I can't remember much about the way DOS stuff used to work, but I'm guessing that the application using the network (it's not TCPIP btw) expects to find an io area at a fixed area in memory.
I did a bit more experimenting. to be able to use EMM386 (and I don't actually know if I need it, but that's what the existing setup has) I need to turn off KVM emulation.
I can get the card to load if I add bus-IDE-BUS after the net card entry in the conf file like this:
net0: ne2k_ISA=0E:44:47:7B:25:61,bridge=vmbr0,bus=IDE-BUS
If I do thus, the packet driver appears to load at the correct point in memory but it reports it's MAC address is FF:FF:FF:FF:FF:FF, which clearly isn't right.
Sadly, any other changes to the configuration via the web gui completely deletes the network card entry.
I have this working in Qemu for Windows (version 0.11.1) so I may have to stick to that, although I'd prefer not to.