All sorts of resources and information on running your Windows machine as a non-administrator.

From Aaron Margosis:

The #1 reason for running as Non-Admin is to limit your exposure.

When you are an Administrator, every program you run has unlimited access to your computer. If malicious or other “undesirable” code finds its way to one of those programs, it also gains unlimited access. A corporate firewall is only partial protection against the hostility of the Internet: you still browse web sites, receive email, or run one or more instant messaging clients or internet-connected games. 

Even if you keep up to date on patches and virus signatures, enable strong security settings, and are extremely careful with attachments, things happen. Let’s say you’re using your favorite search engine and click on a link that looks promising, but which turns out to be a malicious site hosting a zero-day exploit of a vulnerability in the browser you happen to be using, resulting in execution of arbitrary code.