Your best bet is geoIP: http://www.geoiptool.com/en/?IP=32.165.154.5

If you really want to track the person down, you may not to change the gmail password, then monitor the account for further intrusions. Note that a smart intruder will also be watching that page.

In case you have a keylogger, or have been phished, you may want to reformat the hard drive and reinstall everything. Also, if your gmail account is linked to your paypal or other sensitive accounts, you would have to change your passwords on those services as well. Also, secure your wifi.