Update,
After many tests I came to the conclusion that you can run m0n0wall on a NeoWare 3000 without any problems as long you use a RealTek RTL8139 NIC in the PCI slot. This has to do with IRQ sharing of the NIC's.
So to build a nice 2 port m0n0wall Firewall for very little money (eBay) you can use a NeoWare box with an extra Realtek RTL8139 PCI nic, a 64Mb SODIMM, 8Mb CF card + IDE adapter and install M0n0wall on it. Low power and cheap firewall with no fan noise.
Since I need to have a DMZ I need to have 3 NIC's. So I can't use this Neoware box.
If there is a Dual Port NIC based on the Realtek RTL8139 chip set please let me know and I will test this.
Kind Regards,
bt