I have been working with auto desk for close to a month, I ran in to a problem. in the assembly file i cant insert a pipe in to a T coupler, a message pops up saying that I have over constrainded something. can anybody help me? 
Are there any constraints on the pipe currently? If there are you will have to turn them off one-by-one and try inserting each time. One of your constraints is in conflict. Sometimes I remove all constraints on the part in question and start fresh.
If the problem is the other end of the pipe then the two end fittings are not aligned and the insert constraint will give you the same message.
This is what you should do…at the bottom left is a tree system that shows all the components and what constraints have been placed on it. Expand the branches that you are trying to constrain together. Then, go through and delete any random constraints that you do not know why they are there. Then try it again. Often times what happens is a user will put a constraint that either they forgot they put or that didn’t fully work. Then, they try to apply another constraint and it just does not work, giving you an error. Try this approach, and if it doesn’t work, post with more questions.
You could also open the tree like R2 said and look for constraints that have a yellow circle w/ a symbol in the middle (looks like and emoticon almost). The yellow circle basically says that something is wrong or their is an error with the constraint. Delete any constraint w/ one of these on the left side of it.
-Pat
Yea that sounds right… One thing that I do NOT suggest is going through the sketch doctor troubleshooter thing that pops-up. It’s a waste of time, i would just go through the tree of constraints, highlight them and look atthe veiwing window at the faces that are highlighted… Just use common sense, it’s the beauty of Inventor.