Windows' Event Viewer logs a huge number of events, everything from security warnings to application exceptions. Sometimes it can be useful to be informed when one of these events occurs, fortunately, in such a circumstance, it's not difficult to get Windows to shoot you an email.
The default Task Scheduler that comes with Windows is able to react to any event, as long as you know its details.
As gHacks' Martin Brinkmann explains, it's simple enough to set up the appropriate task to run when a user logs in, but sending the email requires a bit of extra work. Depending on what operating system is installed, you have two options: use a third-party program to fire the email, or Microsoft's own Powershell.
For the latter, guides are available online that will sort you out, otherwise, Brinkmann has a solid tutorial for using a utility called Blat that accomplishes the same thing.
Regardless of the avenue you choose, you'll need a working SMTP server — which can be easily sorted with a provider such as Google or Yahoo — to actually send the email.