It gets no simpler than this:
To format your hard disk during Windows 7 installation, you'll need to start, or boot,
your computer using the Windows 7 installation disc.
1. Turn on your computer so that Windows starts normally, insert the Windows 7 installation disc,
and then shut down your computer.
2. Restart your computer.
3. Press any key when prompted, and then follow the instructions that appear.
4. On the Install Windows page, enter your language and other preferences, and then click Next.
5. On the Please read the license terms page, click I accept the license terms, and then click Next.
6. On the Which type of installation do you want? page, click (Custom).
7. On the Where do you want to install Windows? page, click Drive options (Advanced).
8. Click the Partition that you want to change, click the Formatting Option you want to perform,
and then follow the instructions.
9. When you've finished formatting, click Next.
10. Follow the instructions to finish installing Windows 7, which include naming your computer
and setting up the first user account.
Copied from MS and made simpler.