Fixed IP address with Buffalo AirStation G54

I have a Buffalo AirStation G54 wireless G router at my office and
a Linksys WRT54G at home. I carry a laptop back and forth. At home
I set up my laptop to use DHCP with manually assigned IP address. The
router has the default IP address 192.168.1.1 and I have it setup to
hand out addresses in the range 192.168.1.100 - 192.168.1.150 with DHCP,
and I have my laptop set to 192.168.1.2. Everything works fine.

At work, the AirStation has default address 192.168.11.1 but I changed
this to 192.168.1.1. I then tried to setup an identical situation as to
home. However, for some reason it doesn't work. If I use DHCP with
manually assigned IP address, the laptop can't see the router and
doesn't get internet. When I use DHCP (without manually assigned
address), the router assigns my laptop an IP address in the subnet of
the WAN address from the ISP. So if the ISP assigns an address of, say,
69.143.127.168, my laptop might get 69.143.120.1. This seems crazy to
me.

Can anyone tell me what's going on? Why isn't this router creating a
private LAN for me?