if your teacher is giving you an assignment on visio, then let him or the uni provide you with a copy, or simply don't do it.
at uni you're not supposed to be buying illegal software or paying 500$ for original licenses. either THEY provide it or let them not give you homework with it.
Actually you are right, I should have thought about this, I will send him an email and ask him if it would be okay to use
DIA and mentioning your good argument, actually I hate using MS products because there always open source and freeware alternatives but our teacher is a slave for MS he works for them anyways. Thanks battikh :)