Slow Connection on my WES xl module

[knite]

Hi all,
I have WES modules configured and its working perfect encryption and singnal , but i ahve weried problem wondering if some one faced it before!
some laptops connected on high speed bit rate i mean if i copy a file from the inranet in my company it copy the file very fast, in the other hand defrent laptop model if i connect it , it work very slow! laptops like
nx 6110
6710b
mac station G4 notebook
there work real slow, i update the wlan driver, install fresh XP OS, even install a external WLAN card to it like D-Link and Cisco and still the same,
in the other hand I have nc 6320 laptop it work perfect with the internal lan card ot eternal.
i removed encryption just flat now and nothing changed!

any advice