As per the supporting doc the support for vlan in pix has been introduced with 6.3.
do refer this for more info..
If you are looking for the Syntax check the following link. It shows the configuration for single and multi context mode.
If i recall correct you are done with creating the according subinterfaces and associating a vlan. Not sure if you need to create the layer 2 vlans like on the Catalyst IOS version. Don't have 7.x PIX/ASA available currently.
Anyway have a look at the link referring to Pix OS 7.1. It is done different in 7.x then in 6.x.
please see this example
description physical interface to switch. the switch port is configured trunk mode VLAN ID 3 and 5
no ip address
description VLAN 3 for proxy
ip address 126.96.36.199 255.255.255.0
description VLAN 5 for dmz
ip address 188.8.131.52 255.255.255.0