Do you have The frozen throne installed?
Once that is done goto
http://www.getdota.com/ai and get the map with computer support.
In the past the computers have been well above the average player on easy mode.
The needed commands at the very start of the game go...
-apem This enables you to pick any hero from both sides
-arem This enables a random hero given to everyone
Those two are enough for now (the em is for easy mode)
-sdem This enables you a choice of three heroes that you can pick in your circle of power.
That is enough to get you started, let us know how it goes!