Every time you install a new program, update Windows or other software, or even just use your computer as it's intended, you run a small risk of corrupting files that are essential to the smooth operation of your machine. This happens rarely, but it can be a major hassle to recover from if you don't back up your system information regularly (or at least before trying anything extra-risky). Windows 7 makes it easy. Here's how:
Open the Control Panel, then click "System and Security," then "System," then "System protection" on the left.
A small window should pop up with the System Protection tab highlighted. Click "Create..." near the bottom.
Enter a label to help you remember which backup is which.
Windows should now begin creating your restore point. It takes some time, especially if you've been using your computer for a while and installing lots of programs. After a bit, you should get a message informing you that the procedure competed successfully.
To restore your system, repeat step 1, then click "System Restore..." near the top of the pop-up. You'll be asked to select a restore point, and then Windows will roll you back to that time. This means any changes you made to your system, like installing software or changing settings, will be lost, so be careful!
Remember that this doesn't protect your data, like pictures, e-mail, etc. If you want to back them up (and you certainly should), check here for information.