Wireless Problem Dell Notebook

Hi everybody,
I have a strange problem with some dell notebook and a wireless LAN.
The Dell notebook has an integrated wireless card Intel PRO 3945ABG and
the wireless LAN is made by a Cisco Aironet 1131 with EAP WPA TKIP
security.

Well the problem is that Dell notebook connected by wireless can easily
reach any host of the wired network but can't reach each other and
can't reach any host neither in DMZ and nor in Internet. The same
notebook connected by wired LAN can reach any host either in internal,
DMZ and internet.

After some random reeboot notebooks start to reach any host but the
situation in unstable and maybe the day after they stop working again.

The driver version is the latest, the notebook is the Dell Precision
M90.
The Aironet IOS is the 12.3.7.JA4, with wpa authentication.
The radius Server is the w2003 wich is also the DC.

Thank you for helping me.