I just got YDL 4.0 up and running on my powerbook, and I can get an ethernet connection but no wireless. I've gone through the network config, added devices, tweaked with all the options, and tried adding hardware... but nothing.
It's got as far as trying to get an I.P. address, but it comes up telling me that there's no link (cable?)

I'm a newbie, I could be missing something really simple... is there any way to use the command line to find out what hardware Yellow Dog thinks I've got? Could a router firewall prevent the card from reading correctly? What kinds of things can I tinker with to try to get this thing to work?

Welcome to LQ!

As far as I know, Airport cards almost always use a Broadcom chipset, but it doesn't hurt to check. Try running the command lspci in a console and see if the wireless card shows up.

If it is a Broadcom chipset, you're only option is the bcm43xx driver, and that was introduced into the kernel at 2.6.17. If your kernel is older than that, you'll have to update it. If you have a newer kernel, have a look in the output of lsmod and see if bcm43xx is there.