Well in theory yes, that will pasteurize the DME, but what is your recipe? Is is hopped? Are you steeping grains or adding hops? Plus you will still need to cool it down before you pitch the yeast.
There are many other factors to making beer.
-EDIT
Okay, I'm going to assume this is the Coopers kit from your other thread, so yes, you can add the can of extract and the dme to the boiled water. Wait about 10 minutes, add the top off water and if the temp is low enough pitch your yeast.