Rejected network login upon boot

Hi there,
I’m struggling to determine the causes of this problem since a few months, without success.
I’ve got a small network (10 clients with 10.5.3 and 1 mac pro with 10.5.3 server), and the clients are bound to Open Directory.
We also got an airport extreme, to which the mac pro is connected via ethernet, while the clients are wireless. We don’t use 802.1x authentication, just a normal WPA2.

Everytime I turn on one of the clients, when I perform a network login, if the user has a mobile account, it will take something like 2 minutes, then it will log-in and it won’t get any kerberos token, thus asking for a password to connect the shares. If a user is just a network user, it will be simply locked out from the machine, and the only way to logon is to use a local user, login so that the wifi starts up, then logout and re-login again. Same for mobile accounts, after a logout/login they will connect properly to all shares etc.

So apparently the problem is that the wifi doesn’t start at boot, but as soon as a user logs in, the computer stays connected, and it’s possible to perform further network logins without problems.

Do you have any suggestion for me? I can’t find any docs on the internet about this problem 😥

Thanks a lot,
Max