Doing either a quick or full format does not remove any data at all; the only way to over-write data is to do a wipe of the entire HDD; if you want the best possible space to do a real clean install to.

Note
Contrary to popular belief, doing a format with Windows 7 does not remove any data at all, it just checks for sector errors and marks the space to be over-written as needed, all the data is still there including all the code from previous/failed installation attempts.
After you have
copied out or made
back-ups of the data you need to save to external media, use Step One of this tutorial at the link below to do a wipe (
secure erase) to the entire Hard Disk Drive / Solid State Drive.
- Then if you do not want to create the new Windows 7 "System Reserved" partition use the outline in Step Two #2 to create, format and mark Active a single 100GB partition to do the installation to.
- If you do want to create the "System Reserved" partition use the outline in Step Two #3 to create, format and mark Active the System Reserved partition and then create and format the 100GB partition to do the installation to.
Either way, running the "clean all" then creating and formatting the partition(s) using diskpart will get you the best possible space to do a
clean install of Windows 7 to; you can always
extend the Windows partition to include the remaining unallocated space on the HDD / SSD or
create additional partitions after the installation completes if you choose.
SSD / HDD : Optimize for Windows Reinstallation