This is not a step-by-step or even a complete set of instructions. It took me quite a while to get it working back when there was no Knoppix 5. The device names are different on 5 and there is something different needed on the commands. Anyway, FWIW...

WPC54G has multiple hardware versions. Earlier versions use Linux but Linksys was forced to provide their code under GPL and some people claim you can make old Linksys hardware work like more expensive stuff by flashing in some updates. So, more recent versions of Linksys hardware uses a real-time OS instead of Linux. Maybe your version uses Linux, maybe it uses a real-time OS, or maybe it is something else. My version is V3 and this works for it. My router is version V5 and that makes a difference for encryption.

Use lspci to check if your card is even working properly. You should see a BCM 4318 somewhere in the list. If not, then you have a different card version. It may still have a V3 label because Linksys does not change version labels for all configuration changes. I specifically bought this one with a package label that says it supports WPA2 but there are older V3 boxes that do not say that. Maybe the label means nothing because the WPA2 support is in Windows SP2 or maybe it is different hardware or different firmware. Once again FWIW ...

To get WPC54G working unencrypted with Knoppix 4 is relatively easy. I found some good instructions for Ubuntu using google and they worked well. You need to use ndiswrapper and do a modprobe. I was not interested in unencrypted wireless so I only ran that way for short periods to make progress to the next step. It has been a while and I tried a number of different things but this a Live CD and I never saved anything other than some files on my Windows C drive. I always put them there using a USB pendrive because I did not want to risk trashing the NTFS partition and there were many warnings about flaky support for NTFS. YMMV

To get encrypted support working might require an update from Linksys. One posting stated that, so I got the latest version of firmware and drivers that supports V3 of the card. Be careful getting updates from Linksys because you need to match your version of the card. It will be easiest to do this using Internet Explorer on a Windows machine because the web page has some active content that does not work well with my version of Firefox. Again YMMV.

So, here is my script that I have in a folder on Windows. I mount the file system read only, go into the directory, become root and run it:
#!/bin/sh
#
# Knoppix 4 wireless configuration script
#
# This needs to run as root.
#
# debug notes:
# 1) can run lspci to check if card is working - should see bcm 4318 somewhere in list
# 2) use dmesg to check error log
# 3) ndiswrapper -l shows currently loaded ndis compatible drivers
#
ndiswrapper -i LSBCMNDS.inf
modprobe ndiswrapper
#wpa_supplicant -c wpa_supplicant.conf -dd -Dndiswrapper -iwlan0 -K
wpa_supplicant -c wpa_supplicant.conf -Dndiswrapper -iwlan0 -B
pump -i wlan0
#ifup wlan0
wavemon

I am not sure why I had a -K and went to the -B on the WPA supplicant. Maybe it is debug notes or maybe it was a change from one version of the code to another. Remember that I said it took a while to get it working the first time. If you want to run unencrypted (not advisable but may be unavoidable in some apartment complexes) then you do not need to get the wpa_supplicant stuff working.

My current version does not do the ifup but it was needed earlier. I have no idea why it was needed earlier but then was removed. If it did no harm to have it in then I probably would not have removed it. It could be that I needed it for KNOPPIX 3 or maybe an update from Linksys caused different behavior. Maybe I switched from ifup to pump. Sorry I did not keep better notes but I was trying to find something that worked and had read that there were updates in Debian that made wireless work out of the box. So, I expected KNOPPIX 5 or Ubuntu or some other distro to "just work" and did not plan to use this setup as long as I have.

The LSCMNDS.inf file comes straight from Linksys - no customization by me. It is different than other LSCMNDS versions and does not match the version I use for Windows XP. Windows was working and I saw no reason to mess with it. I had enough trouble getting the WPC54G to work the first time with Windows and had to spend time on the phone with Linksys support. They told me that following the instructions in the box and using their CD was a mistake - so we had to undo that before we could let Windows XP SP2 take care of it with a couple small tweaks and few reboots. According to support, the stuff in the box applied to systems before SP2 but WPA2 only works with SP2 and the box label that says it supports WPA2 means that the hardware will work with SP2 but only if you ignore the instructions and just plug it in and let Windows reboot a few times as it discovers the device and configures itself (and downloads updates over ethernet plugged in because wireless is not working yet!)

So ... enough rambling ... that should give you enough to get started if you do not want to take the suggestion to install something else. Remember that the script above is used with a Live CD boot and that is different from an HD install boot in ways that might make a difference.