If you run Redhat Enterprise Linux 3 (RHEL 3) in a Virtual Machine, using VMWare ESX 3.5, network interfaces will work if you assign a static IP address to each of them, but if you use DHCP, it will not work, showing up a message like:
no link present. Check Cable?
This is a known issue for VMWare, published on Knowledgebase Article 977:
Edit (for eth0):
Then execute: $ifup eth0
Repeat the process for every NIC you need to use DHCP