I have an apple tv. My macbook pro mid 2010 does not support airplay but I want to mirror the monitor onto my tv screen. How can I do this?

There are 3rd party products such as Airparrot that do the same thing, just don't expect them to work as well.

I would recommend upgrading your laptop. Does your current laptop have an HDMI port? If so, connect your Mac to your TV with an HDMI cable. Your TV must be compatible, if it is, you will have to understand that it will be no where near the quality of AirPlay.