"does IP-Masquerade can work with ONLY one network card ?"
It can, but it is not recommended. From the IP Masquerade HOWTO:
"With the "IP Alias" kernel feature, users can setup multiple aliased interfaces such as eth0:1, eth0:2, etc but its is NOT recommended to use aliased interfaces for IP Masquerading. Why? Providing a secure firewall becomes very difficult with a single NIC card. In addition to this, you will experience an abnormal amount of errors on this link since incoming packets will almost simultaneously be sent out at the same time"
So with eth cards costing $10 I would go buy one, and save some grief later on. You will also need a length of ethernet crossover cable, available at any computer store.
Read the howto carefully, I used it to set up my own box a few days ago and it works excellant. Good luck.
http://www.tldp.org/HOWTO/IP-Masquer...WTO/index.html