WPA2 login slow

I have setup WPA2 authentication with XP to an IAS radius server. All works
fine when XP configured for user authentication only. My problem is trying to
get computer authentication to work first, then allow the user to logon to
the system.
It appears the computer authenticates, if I wait some time(as I know I
should) I login with user crediedntials and soemtimes the login works and
somtimes it does not. It also appears that when it does work, the login
scripts do not run. Also it is extremely slow during logon processes.
I have tried registry changes for authenticating the computer only, this
works great and the user can logon without a problem. However I want to be
able to have different users logon to a WPA2 laptop and each authenticate
according to a group in AD.
Any one done this? Experences and suggestions please as I know this would
help many others.
Cheers