Aggregating network interfaces
Using more than one hard drive to achieve better performance and fault tolerance is very common. Less well known is that it's also possible to aggregate more than one network interface into a single logical interface. In Linux, this is handled by the bonding driver. Benefits of doing this are much the same as the benefits of aggregating discs using RAID: if one device dies, your server carries on working and by using two devices in parallel, performance can be improved.
The first thing you need is two network interfaces. It's not entirely uncommon for a server to come with two: one gigabit card on the motherboard and a separate 100 Mb PCI card. You will need to ensure that the Linux kernel has recognised both interfaces. Running /sbin/ifconfig -a lists network interfaces. Typically, you should see both eth0 and eth1 interfaces. If not, make sure that the modules for both interfaces have been compiled for your kernel and loaded. You may need to do something special if both devices use the same driver.