I would really consider an overland bus mate, its probably more expensive but at least its safe and accomodation and food is chucked in. By car yourself your looking at going through possibly Afghanistan and other nasty countries which do not recognise international driving licences and don't appreciate you being there in general.
If you do go yourself take a lot of time to plan it, check with the embassies, plan your route carefully, not worth going the shortest route which could also be the most dangerous. On the timing i reckon if you made the odd stop over and things you could do it in around a month, probably a good idea though to then sell the car and fly back lol.
<a class="postlink" href="http://www.odysseyoverland.co.uk/expeditions.htm" onclick="window.open(this.href);return false;">http://www.odysseyoverland.co.uk/expeditions.htm</a>