Friend sometimes and dependiong on the company after interview it could be 1 week or several weeks. Even sometimes you get a response on the same day you were interviewed.

A follow up call or a follow up email is advisable just to let them know you are interested in the position and that you are willing to think about a formal proposal to work with them.

But this will be up to your mood and desire to work with them. Give it a try, you never know, the worst that could happen is the to tell you tha position has already been filled but then you have the choice not to keep on waiting on them but to look for other oportunities in the job market.

And remember "if a door closes a thousand windows open!!"