I've searched the forum for several hours, and I'm starting to think that my problem is not that common:

I have an Intel 3945ABG wireless mini pcie card on my laptop, which is not detected by Slackware 12(should be kernel 2.6.21.5 but I can't completely remember as I'm posting this on windows).
The compilation and installation work fine, and ipw3945(1.2.2) as well as ieee80211(1.2.18) show up when I lsmod. After moving the ipw3945d(1.2.22) daemon into /sbin, however, it freezes the system after several seconds after displaying an error message with "Oops!" in it.
The interface even shows up with if/iwconfig, the ucode(1.14.2) being in /lib/firmware/, only the daemon isn't running for it to be used properly.

(The actual error message will be placed here as soon as I get a chance to write it down).

Any help will be greatly appreciated :-D

I finally got around to copying the error message:

BUG: unable to handle kernel NULL pointer dereference at virtual address 000002e4
printing eip:
*pde = 00000000
Oops: 0000 [#1]
SMP
Modules linked in: snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq_device snd_pcm_oss snd_mixer_oss

I know these are refer to sound devices, but the error only shows up after ipw3945d has been running for less than a minute. I'll try to find a different version of the daemon and see if that changes anything.