first off, I only know how to do this in Windows, and it is different for each version thereof.
usually, it's in...
C:\Windows or C:\Winnt if you have XP Pro.
then, go to System32, Drivers,etc and, if the Hosts file is not in there, then open the Hosts folder.
note that you may need to have it show hidden files to be able to actually see it. then, it'll probably looks like..
Code:
# Copyright (c) 1993-2006 Microsoft Corp.
#
# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
#
# This file contains the mappings of IP addresses to host names. Each
# entry should be kept on an individual line. The IP address should
# be placed in the first column followed by the corresponding host name.
# The IP address and the host name should be separated by at least one
# space.
#
# Additionally, comments (such as these) may be inserted on individual
# lines or following the machine name denoted by a '#' symbol.
#
# For example:
#
# 102.54.94.97 rhino.acme.com # source server
# 38.25.63.10 x.acme.com # x client host
127.0.0.1 localhost
::1 localhost
78.47.99.206 www.aspiesforfreedom.com
something like that, methinks once you've edited it.