Totally wireless

Set the laptop up to join the ad-hoc wireless network between the two WRT54g units. There was a small hitch in that an IP address wasn't allocated to the laptop, so I set a manual default fallback one.

An ADSLguide speed test from the laptop gave :-

Direction Actual Speed True Speed (estimated)
Downstream 1854 Kbps (231.8 KB/sec) 2002 Kbps (inc. overheads)
Upstream 125 Kbps (15.6 KB/sec) 135 Kbps (inc. overheads)

a tracert shows :-

C:\Documents and Settings\Phil>tracert 10.0.0.2

Tracing route to BelkinModem.yarwell.demon.co.uk [10.0.0.2]
over a maximum of 30 hops:

1 1 ms 1 ms 1 ms 192.168.3.10
2 2 ms 2 ms 3 ms 192.168.3.1
3 3 ms 3 ms 3 ms BelkinModem.yarwell.demon.co.uk [10.0.0.2]

Trace complete.

So we can see that the upstairs WRT is routing the packets to the downstairs and hence on the wired LAN to the Belkin ADSL modem / router. The upstairs unit 192.168.3.10 is set as the default gateway on the laptop, and 10.0.0.2 is the DNS server :-

Ethernet adapter Wireless Network Connection 5:

Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : Belkin 802.11g Network Adapter
Physical Address. . . . . . . . . : 00-30-BD-92-67-13
Dhcp Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
Autoconfiguration IP Address. . . : 192.168.3.5
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 192.168.3.10
DNS Servers . . . . . . . . . . . : 10.0.0.2

I guess the DHCP is the only thing to fix. The ad-hoc networking is a bit invisible to the user, apart from setting the default gateway there isn't any sense of connecting to a particular ad-hoc peer.