Your Welcome.Therefore I would like to say a big THANK YOU.
However I have one question that has not been covered here. I wish to check the slot before adding the appointment i.e. I wish to check whether the slot is busy or free and if busy check the type of category used.
i have never done what you are talking about as I always send the appointment item and then let the person decide whether to accept or not.
But I had a look at the Appointment object.
http://msdn.microsoft.com/en-gb/library/aa210899(office.11).aspx
I like the http://msdn.microsoft.com/en-gb/library/aa211808(office.11).aspx conflicts collection which has a little example there. You can then get a conflict object and check it. I am not sure if this is only going to show the conflicts of outlook on the computer this code is working or on all conflicts.
Another way is to use your email addresses to get a Recipient and then use the freebusy method. http://msdn.microsoft.com/en-gb/library/aa220097(office.11).aspx