ISA 2004 configuration DHCP, DNS , NAT

Hello Everyone!

I am new to ISA and trying to install it in my office. we have about 20 client machines.
We have AD domain with 2 DC and active directory integrated DNS on both DC.
The DNS servers have ISP's DNS server as forwarders.

We have a DSL router with one public IP and a block of IPs (used for web sites by our web server)

The DSL router acts as DHCP also and as NAT .

we use 192.168.1.0 network internally.

I have gone through the ISA configuration guide and quick start guide and have a few questions.

1. I plan to set up my ISA as

DSL -> router -> ISA -> switch ->patch panel-> clients and servers... Am i right ?

2. Quick start guide says , i install DNS on ISA and configure it as STUB zone with my AD DNS servers. I did that and put ISP's DNS as forwarder on DNS on ISA. Do i Have to change anything on my AD (internal) DNS servers also ?

3. What about DHCP. Can i still use my DSL router as DHCP with current configuration ? or would i have to use a DHCP server on internal network? or do i have to install DHCP on ISA ?

4. How do i go about using NAT ? Can i still use my router ? or will have to configure somewhere else ?  

This is for now to get me started. i will probably have more questions as i get started with this.

Thanks