Hi kiran,
You can perform the following
a) Create a GPO on windows 2008 AD
b) Edit the GPO and select the following
Computer Configuration > Security Settings. You'll notice a node called Wireless Network (IEEE 802.11) Policies which you can modify
accordingly
c) create a network policy rule and apply to clients.
But there is a catch , if you check the xp clients there is no wirless GPO available, for which you need to copy files from windows 2008 and then
register them into xp
such as
then regsvr32 wlsnp.dll