3COM Internet Firewall

I have 3Com Internet Firewall 25 and OfficeConnect 612 ADSL.

My ADSL is PPOA with IP assigned by ISP on connection.

I don't seem to be able to get things working.

COnfigure
ADSL LAN Address 192.168.100.1

F/W LAN Address 192.168.1.254
F/W WAN Address 192.168.100.1

Have tried NAT DHCP, NAT, Standard

none see, to work. Any pointers appreciated