Got a lot of help here to get it work, so here's my giving back.
My OS: Slackware 10.0
Kernel: 2.4.26
Card: D-Link DWL520 Revision D, with a realtek chipset

Sorry I can't post an url since the system said I got to have posted at least five posts to do that. It should be easy to use google to find their websites.
1. Download ndiswrapper 0.8 from ndiswrapper
2. Download the realtek WindowsXP driver from realtek, choose RTL8180L
3. extract ndiswrapper: tar xvfz ndiswrapper-0.8.tar.gz
4. cd to the ndiswrapper-0.8 folder
5. Compile and install
As root run
> make install
6. Install your windows driver
> ndiswrapper -i </path/to/NET8180.inf>
After installing you can run
> ndiswrapper -l
Output on my machine:
> Installed ndis drivers:
> net8180 present
Where "present" means that I have a PCI-device present that can be used with the driver net8180.
7. Load module
> modprobe ndiswrapper.
8. Configure interface
Use iwconfig to configure wireless network interface. First, locate the wireless interface:
> iwconfig
This will print the wireless interface (e.g., wlan0 on my machine). In the examples below wlan0 is used; replace wlan0 with the interface reported by iwconfig above.
At this time iwconfig shows my card has already connected to the router. Everything like Mode, ESSID,..., is set except an IP address. Maybe because I'm also using this card under WinXP so it's already configured? I'm not sure. You may have to configure it yourself.
9. Bring the network up
> ifconfig wlan0 up
10. Enable dhcp client daemon
> dhcpcd wlan0
Now if you use
> ifconfig
You will see wlan0 is up with an IP address. And you can use your internet now.
11. Automate
Once everything works fine you can write the correct modeprobe settings to
load ndiswrapper automatically by running
> ndiswrapper -m
Now everytime after reboot you can use
> ifconfig wlan0 up
> dhcpcd wlan0
to bring up your network. If you also want this to be automated, add them to rc.local.
# cat /etc/rc.d/rc.local
#!/bin/sh
#
# /etc/rc.d/rc.local: Local system initialization script.
#
# Put any local setup commands in here:
ifconfig wlan0 up
dhcpcd wlan0

Please refer to the INSTALL file in the ndiswrapper directory if you have questions.