1. Boot from the Windows 7 DVD
2. Click Install Now
3. When the option is displayed to select an installation type, click (Custom Advanced)
4. select the disk partition where you would like to install Windows 7 Click Next.
You will receive the following warning: Do not click anything named Format or Delete or Partition. So even doing a custom install, your personal files are still preserved. Click OK
Setup will now start the installation. During the installation, your machine will be restarted several times.
When the installation is complete, you can complete the Out of Box experience such as selecting your laptop, create a username, password, your time zone. You can then proceed to download the latest updates for Windows and reinstall your applications and drivers.
You can then recover your personal files from the Windows.old folder and reinstall all your applications and drivers.