Hi,
You need to add following package to attach and detach slave interfaces to a bonding device
Code:
sudo apt-get update && apt-get install ifenslave-2.6
Enable bond0
Now setup bonding mode for Round-robin policy:
Code:
vi /etc/modprobe.d/arch/i386
Code:
alias bond0 bonding
options bonding mode=0 miimon=100
Now open /etc/network/interfaces and modify as follows:
Code:
auto lo
iface lo inet loopback1
auto bond0
iface bond0 inet static
address 192.168.1.100
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
gateway 192.168.1.254
post-up ifenslave bond0 eth0 eth1
And just restart computer and you are done

test the same:
Code:
less /proc/net/bonding/bond0
ifconfig -a
See following links for more info:
Linux Ethernet Bonding Driver HOWTO
Debian Administration :: Aggregating network interfaces
Linux bond or team multiple network interfaces (NIC) into single interface | nixCraft