Use the "Unplug or eject Hardware" icon on the taskbar to stop the card. When it's ready, you get a pop-up box saying it's OK to remove the card.
Beware, when you plug it back in, it may not connect to network resources properly, and you may need to log off/log on to re-estabilsh the connections.
Also, if you plug it into a different PCMCIA slot, it may load another set of drivers. It depends on the hardware detection, and the internal driver setup.
Howard