I'm using a a WG511 wireless card and yes you need to use the prism54 driver. The problem is, mandrake does not include the firmware need for the driver to interact with the card (for licensing issues i assume).
So, to get it to work, first you need to download this file...
http://prism54.org/~mcgrof/firmware/isl3890
And then place it into the folder..
/usr/lib/hotplug/firmware/
(if the folder doens't exist, just create it).
Just reboot, it should work fine. If not, post and i'll try to help more.