Cisco Pix 501 basic VPN question

I am new at cisco and want to create a VPN with my ADSL connection.

I've configured the cisco locally from the inside network and it works,I can connect with my vpn client with Ipsec UDP and ping other devices

But when I connect the pix to the ADSL modem and try to connect from dailup internet connection I cannot connect with the client I can ping the adsl modem and configured the WAN address in the vpn client but the connection doesn't seem to go through the adsl modem.

Which things do I need to check on the ADSL modem to get it working (I've read some articles about NAT, IP Spoofing??)

I don not have access to the config right now but, i've configured the outside of the pix within the subnet of the inside of the ADSL modem/router (192.168.2.x) Is it possible to enable IP spoofing on the modem and configure the outside of the PIX with the fixed WAN address??

you have to do a static nat mapping for the outside interface of the pix on the adsl router.