That is the output of his lspci.
There is no support in the 2.6.26 kernel.
This is the same device from 2.6.32 kernel lspci:
PCI: 168C:002A Atheros Communications Inc. AR928X Wireless Network Adapter (PCI-Express)
It's not supported by madwifi or ath5k anyway (which is probably why it's not working), it's an ath9k device in fact.
To get this working correctly you will need the 2.6.32 lenny backports kernel.
Ensure you are tracking the debian archive in your sources.list and add the backports archive repo as well.
You should then be able to install a 2.6.32 kernel and it should just work.
If you plan to use networkmanager you should also get that from backports as the version in lenny was rubbish...
Of course ideally you should be upgrading to squeeze as lenny is an unsupported release.