Then boot into installer DVD or flash stick burned or written using tool and latest ISO for your licensed OS version here.
At first installer screen Press Shift + F10 to open a Command Box, type:
SEL DIS 0 (after confirming Windows 7 target HD #)
CREATE PARTITION PRIMARY SIZE=102400 (for 100gb partition, adjust as desired)
FORMAT FS=NTFS LABEL="WINDOWS 7"
Next click Install Now to Clean Install Windows 7
to the partition you created. If it fails then report back at which step and the verbatim error message.