there are 100 vlans (layer 3) and 20 Layre2 vlans on the core switch.
i'd like to add them to FWSM without NATing, what can i do? do i use nat 0? and how can i add the layer 2 vlans to FWSM (without having IP address for them)?
You have to understand that you can have only ONE Layer3 Routing Interface in VLAN network. If you want to use the FWSM you have to shutdown all your Layer3 Vlan interfaces on your switch! So your Switch will only do Layer2 work. HSRP you can't do in this constellation.
You need 2 FWSM. One in the first Chassi and one in the second and than you have to configuring Failover on the FWSM.
I hope I could help you.