I've been struggling for a month to get wireless working
again after I upgraded to Mandrake 9.0. Most of the
problems were my own, and the fact that the wireless
card died halfway through the processes (it's very hard
to get a dead card to work).

Finally I managed to get it to work again, but throughput
was very slow.

I finally found out what it is.

Prelude.

This security server might enhance security but it
completely sucks the performance out of your wireless
connection.

Go to the control center, system, services and stop it.
In my case network performance improved immensely.