I use this exact setup and have no problems at all. Enable ICS on the first machine, the card connected to the internet will obtain its own IP. Once you enable ICS on the internet card in the main machine, the second card will be given an IP of 192.168.0.1
In the second machine you need 2 NIC's, connect one to the main machine the other connects to the 360.
Bridge the 2 cards together so they both share the same IP address, using 192.168.0.2 would be ideal. It should look like this.
Second Machine
IP Address: 192.168.0.2
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.0.1 (the card with ICS enabled)
DNS Server: 192.168.0.1 (same as above)
Then for the 360
IP Address: 192.168.0.3
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.0.1 (the card with ICS enabled)
DNS Server: 192.168.0.1 (same as above)
The 360 will then go through the second machine and straight to the DNS server. This is a very cheap setup, the only draw back being you need both machines on.