Connect to a network behind a VPN Remote network

[vmlatorre]

I'd like to know if it is possible to connect to a network which is behind a remote VPN network.

I show the diagram:

|----| |----| |----|
| | | | | |
|NET1|---pix1----INET----pix2---|NET2|----router---|NET3|
| | | | | |
|----| |----| |----|
--------------------------------
VPN

NET1: 10.100.0.0/16
NET2: 192.168.1.0/24
NET3: 172.20.1.0/24

I setup a LAN-TO-LAN VPN with two Cisco PIX 501.
I can connect without any problem in these ways:
"from NET1 to NET2" and "from NET2 to NET1".

But my problem is that I want to connect from NET1 to NET3 through the VPN tunnel but I can't do it.

I don't know what I have to do in the pix1 and pix2 configurations.

Thanks.