Which can be done as Eljay said, by using the MyStatusChange... He didn't missed something
The further
tools to pull this off are on the forum already and starts with 'p' and ends with 'atching'... with a prefix like 'soft'
(this is at least one way to detect becomming idle)
PS: You wont be idle as long as you're working on the PC. Idle in Messenger means idle on the PC, thus not only in Messenger.