When I was in Iran last October there was talk about the Iranian Pakistani border being closed so u would have to check that out if u intend to travel overland that route.
Here is a thread about Pakistan that somebody else started. It may have useful information for u. Also pay particular attention to the news about Pakistan at the moment.
I think u will find Iran relatively safe to travel accross. If u adapt the Islamic dress and behaviour code while u are there u are unlikely to have problems with police or people in Iran.
I dont know exactly about Turkey but check the current safety situation at the Iranian Turkish border. The Iranian government say they are going to pour money into border security for Iran. I dont know exactly what that will involve.
[ Edit: Edited on Dec 28, 2007, at 5:31 AM by Mel. ]