Finding the IP address will not tell you how to find the senders actual home address - you are wasting your time trying that route.
It is pretty much impossible to draw any direct correlation between an IP address and a real-world physical geographic location (house or street or district). They are not connected.
IF you have threatening emails then report them to the post master of the emailer. Look at the bit after the "@" sign and send an email to "postmaster@" that domain/ISP/mail service.
If they are coming from a dedicated domain (i.e.
[email protected]) then a whois lookup of the domain name might give you some info about the owner/registrant, but not much if registered via an agent or 3rd party. Google "whois" for more info.