Internet Connection Sharing works with crossover-cable but not Wireless. Network Wizard doesn't complete.

I'm trying to network a desktop and laptop so that each can see the other's
shares and the laptop can connect to the Internet via the desktop's dial-up
modem. Both run XP Home.

Using a crossover cable, everything works. When I try to use wireless kit
(Belkin 6001 PCI card, and Belkin 6020 PCMCIA card in ad-hoc mode, no
encryption) the two devices can see each other, but the laptop can't see the
Internet. I've disabled the McAfee firewall on the desktop.

Worse, having found that disabling and re-enabling ICS has no effect, I ran
the Networking Wizard on the desktop. That ran for 30 minutes before I
forced a reboot, after which the dial-up connection would connect, but could
not find any site (an apparent DNS problem). Only a system restore would
retrieve the situation.

I'd be really grateful for any pointers!

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