That's a kernel recompile, I'm afraid.
Under Device Drivers > Networking Support > Wireless LAN Drivers (non ham-radio). For the Atheros chipset, you just need to enable the top option there (Wireless LAN Drivers and Wireless Extensions), as the MadWiFi drivers handle everything else.
Also, you should make sure you've got wireless tools installed. I know that they aren't installed by default on some versions of Slack, unless you did a "complete install". They're in the N package, if you need 'em.