There is really nothing to be tweaked. Check the driver versions on the wireless card and see if it is pretty old or new. 30sec is a long time, are the users by an access point or pretty far away? Even if you try an open authentication, will the users still take that long to associate? Is it 30sec to associate or to get an ip address? If it is an ip address then it could be an issue on the network.
It would be helpful to know exactly which phases of the conversation are slowing things down- whether it's the initial association, the authentication phase, DHCP, or what.
My first step would be to set up an open SSID (no security) and try to connect with a static IP, and see how long that takes. Then tweak step-by-step towards your desired final configuration and see where things slow down.
If a static/open connection is slow, then that at least lets you know that the association phase itself is the slow part, and you can troubleshoot from there.
Since your using WZC I'll assume you are using either PEAP or EAP-TLS. You should make sure the default EAP timers on the controller were adjusted. The defaults can be to low for the certificate negotiation during the first phase of authentication.
The next thing to do is to run "debug client..." on the controller to see where the failure is occurring. This will help you determine where to look next.
Also make sure you have all the latest patches on the client. If you are running XP make sure it has SP3. There were a number of WZC fixes in this SP.