Blocking URLs in XP

You can edit (by Notepad) the file called <b><font color=red>host</b></font color=red> (w/o any extension) in <b>Windows\System32\Drivers\Etc</b>.
Here is an example of the file,
#############################################################

# Copyright (c) 1993-1999 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.
# <i><font color=red>The IP address and the host name should be separated by at least one
# space</i></font color=red>.
#
# 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

############################################################

You can block some websites by redirecting them to null IP 127.0.0.1. For example, if you want to block www.kaaza.com, www.hornygirls.com, add them below the last line (remember, 1 line for each one)
127.0.0.1 www.kazaa.com
127.0.0.1 www.hornygirls.com
<b><font color=blue>NOTE</b></font color=blue>: when saving it, making sure it has no extension at all because Notepad tends to add the extension .txt.

Good or Bad have no meaning at all, depends on what your point of view is.