Be careful with looking at Software like ACad on Ebay. AutoDesk has in the EULA (End User Lisence Agreement) that the only way to legally transfer ownership of the software is through change of ownership of a company...not sure of the exacts. They changed this about 6-8 years ago. So legally AutoCAD should not be available on Ebay.
Also cb68 is correct right now you can only by the Inventor AIS or AIP which come with ACAD and MDTDX.
Again be careful with software sales on Ebay....in most cases it is illegal.
I believe that the EULA (End User Lisence Agreement) Autodesk and other software companies use may be illegal by it self.
I have a first hand experience with an original disks I bought second hand. One day I have recieved a letter from a lawyer representing the software organization. After I showed the lawyer the original disk and told him I bought it second hand and offered to return it to the company or discontiue using it, he told me that I can continue use it legally because I payed for it.
I know about a second case with Solidworks where a company received a legal copy as a payment for a job. When they tried to upgrade it, Autodesk representative refuesed because it was not transfered according to the EULA but they said that they can continue use it.
Just imagine a case that a company or a person gone broke or died and all his belongings sold in a garage sale. If someone buys the software and sometimes it passed few hand, is it logical that the software is lost? It is more logic to say that the rights were passed to the buyer when he payed for it.
Imagine that you buy a car or a book and you can not sell it without the permission of the company who made or printed it. As long as only one individual use it and has the original disks in his possesion I do not think the software company can legaly have a say about it.
If you look at the arguments that E-bay give after they remove auch auctions they say: The auction was discontinued because the software company claims that it MAY infringe their right. Notice the "MAY".
I believe that such a EULA is against humen rights to own a aproperty and do with it what he likes as long as he does not duplicate it and sells duplicates.
It will interesting to here what others say about it and bring from their experience.
You may be correct there...it seems that is a rather grey area and the software companies basically say that you have the right to use the software by buying it. They say you don't own it, you just own the right to use it. There are many threads about this in many forums. And as you say it will be interesting to hear what others say about it.