Yes.
Yes, formatting a computer hard drive will delete the operating system.
Yes.
Formatting, there's no easier way to clean a Hard drive as new like formatting
If they are on separate hard drives you can generally just delete/format the hard drive with the OS that you do not wish to keep. If they are on separate partitions on the same hard drive you may have to reinstall the bootloader after deleting/formatting the partition.
Yes, Surely it will remove everything on hard drive. Formatting a hard drive means to remove everything on hard drive. If you are formatting only a specific drive like C:\ or D:\ then the data in only that drive will be removed.
You can manually go through the file structure and the registry and delete the files and registry keys belonging to the program. You can usually find out which files to delete and where they are by searching "manual uninstall [game name here]".
Of course, copy all your programs and files you need from the old hard drive and put it on your new hard drive BEFORE formatting the old hard drive. Formatting your hard drive will mean losing everything and a slim chance of getting it all back.
To format a hard drive means to delete any information on the drive and to set up a file system so Windows 7 can read from it and write data to it.
Formatting your hard disk for the PS3 will erase everything on it. If you are adding a hard disk to your PS3 it will prepare the drive for the system.
Yes it will, but it will also remove EVERYTHING on the drive; your personal files, settings, programs, even your operating system. Don't attempt to format your hard drive unless A) You are prepared to loose everything on the drive AND you have experience installing Windows or another operating system. B) It is a secondary drive (such as an external hard drive) which has no system files AND you are prepared to loose everything on the drive.
By formatting the hard drive.
You can completely clear your external hard drive by formatting it.