apt-get install vlan modprobe 8021q vconfig add eth0 4
or in network configuration script:
/etc/network/interfaces
# VLAN 4 auto vlan4 iface vlan4 inet static address 192.168.0.8 netmask 255.255.255.192 network 192.168.0.0 broadcast 192.168.0.63 mtu 1500 vlan_raw_device eth0