Can't you use the 4th NIC port for the new LAN?

As Bob said, Masquerading to a second IP won't work until 7.5.

VLANs work fine though; see my sig below.

Barry

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http://DealBert.net
Home & business end-user since v1.x

• ASL 6.3x, HP DL145 Dual Opteron, 1GB RAM, 6 gigE NICs, 50-IP Platinum License
  
• ASL 7.3x, Dell PE1550 Dual PIII 1GHz, 1GB RAM, 2 NICs, 50-IP Platinum License
  
• ASL 7.5x, 17-watt fanless mini-ITX system: MSI IM-945GSE-A Atom n270, 2GB RAM, Morex T3310 case. 2 Intel GigE, 3 VLANs. 80G 5200rpm 2.5" HD
  Netgear GS108T gigE VLAN switch & Linksys WRT54G WAP
  Total network infrastructure: 27 watts. 100-IP Home User. FiOS 10mb/2mb