If your friend had you visit a site that looked funny example: http://123.45.678.910.com then you probably ended up getting scanned by his computer... however if you did want to get even you could just copy down that number because its his I.P. also.. I'm guessing he used something like Visual Route to find out where you are... theres something like Visual Route under the Tools and Toys section of this site... however it doesnt give nearly as many details as visual route.
you might want to try using a I.P. spoofer or Firewall from now on when you talk online