Control Panel\All Control Panel Items\Administrative Tools
Press start >> control panel >> Administrative tools >> Task Scheduler
or
Type "scheduler" in the text box over the START button and wait for the search results.
Before we go further I use minerd.exe which comes with the litecoins download program. It's the dos version miner. It also requires your LTC wallet client to be running as well.
Since a picture is worth a thousand words I'll post a series of picture that show how step by step.
Now that you should be in Task Scheduler create a new folder. I called it MINER
After opening the folder MINER I create a new task
Name the task I called mine MINER and if you want add a description I chose to leave it blank.
Then move on to the next tab called triggers then select the button called new at the bottom.
Using the drop down box select Idle
Now move on to the next tab called Actions. Again select the new button at the bottom.
Ok this is where you browse and select your program to have it run when the idle is triggered. The dos program minerd.exe will require arguments to run or it will just exit in a flash. If you're not sure on how to use it there are plenty of LTC threads explaining on how this is done. I believe Graet has a good how to thread.
Add your parameters in the ADD ARGUMENTS box
eg: --algo scrypt --retries --scantime 20 --threads 1 --url
http://litecoinpool.org:9332/ --userpass <username.1>:<password>
Then select OK and you should be done.
There are more options available and its up to you to see what is best. Now as an added observation I have seen it take quite a while before the Idle is triggered. So to test if it works you select the green play button on the side.
Hope that helps