Here are some Steps if you dont want to go into the details on Micrsoft Website.
1. Put the Windows 7 installation/Upgrade disc in the disc drive, and then start the computer (set to boot from CD in BIOS).
2. Press a key when you are prompted.
3. Select a language, a time, a currency, a keyboard or an input method, and then click Next.
4. Click Repair your computer.
5. Click the operating system that you want to repair (Windows 7 in this case), and then click Next.
6. In the System Recovery Options dialog box, click Command Prompt.
7. Once in the command prompt, type exactly Bootrec.exe /FixMbr and then press ENTER. You will see "operation completed successfully." (Doesnt even take a second. Dont be alarmed )
8. Reboot and set BIOS to boot from the HDD again.
GRUB will be overwritten in step 7 and Windows bootloader will once again take control of loading your OS(s).