Windows 2003 Server 2 NIC/Network Cards Multi-homed connection

Make sure you either have or can install Routing & Remote Access (should be in Administrative Tools)
If you need to install it, just do so with basic NAT/Firewall checked (one of the options required to install RRAS - Routing and Remote Access Service), but we're not going to use NAT.

Remove your gateways from your adapters (by going to your NIC->TCP/IP Properties->Advanced->Gateways->Remove (hopefully you can get my drift))

In the RRAS snap-in, right click on Static Routes and add a new route.
(I'm going to assume that your LAN connections are named "Network Card 1" and "Network Card 2" respectively for ease of typing)
Set this up:
Interface: Network Card 1
Destination: 0.0.0.0
Network mask: 255.255.255.255
Gateway: 192.168.0.1
Metric: 1

Click ok, and right-click "Static routes" and add another new route:
Set this up:
Interface: Network Card 2
Destination: 0.0.0.0
Network mask: 255.255.255.255
Gateway: 192.168.0.2
Metric: 1

Click "OK" and then right-click on "static routes" and click "show ip table"
make a note/screenshot of it as it is now

Go back to your network adapter
properties, go to the "Network Card 1" properties
Go to TCP/IP Properties->Advanced->Gateways->"Add"
Gateway: 192.168.0.1
Automatic Metric: UNCHECKED
Metric: 20
Close out of that

go to the "Network Card 2" properties
Go to TCP/IP Properties->Advanced->Gateways->"Add"
Gateway: 192.168.0.2
Automatic Metric: UNCHECKED
Metric: 20

Now get a new list of the routes in your IP routing table by going into the RRAS snap-in, right click on "static routes" and click "show ip routing table"
You should have at the top, something like this (the first 4 lines are the critical ones, if these aren't right, re-try the order in which you setup the static routes & add the gateways)

Destination Network Mask Gateway Interface Metric Protocol
0.0.0.0 255.255.255.255 192.168.0.1 Network Card 1 1 Static (non...)
0.0.0.0 255.255.255.255 192.168.0.2 Network Card 2 1 Static (non...)
0.0.0.0 0.0.0.0 192.168.0.1 Network Card 1 20 Network Mgmt
0.0.0.0 0.0.0.0 192.168.0.2 Network Card 2 20 Network Mgmt

Be sure to make your destination NAT on your routers MATCH from router to IP resepectively, or the whole thing won't work, ie:
router: 192.168.0.1 needs to forward traffic to 192.168.0.5
router: 192.168.0.2 needs to forward traffic to 192.168.0.4

Essentially what you're doing is bonding a gateway to a NIC. This may work for you, it has definately worked for me when I needed to setup a web server that would respond on 2 different public IP's.