Detecting a thin client logon with a logon script

Hi,

My users use Citrix Metaframe to access a remote server, whenever they
logon via Citrix, their logon script executes a second time (first
time when the logon to their local machine) - this takes ages to do
and brings up a whole host of errors as the various drives are already
mapped.
Does anyone know of any Windows Hosting Scrip functionality that can
test if the logon is is happening over a thin-client network and then
run a different script if it is?
Thanks in advance

Phil Teale