You may think that you are reasonably safe as you surf the net, but windows has many gaping flaws that do not protect your privacy, and it it far too easy for a hacker to gain access to your privacy and others to harness your ISP etc. There are some simple steps outlined below which will allow you to surf much safer, as well as guiding you through various tweaks to help you.
http://cotojo.wordpress.com/2007/04/25/protect-your-pc-and-privacy/