You should really reinstall Windows however as you said, you don't have the CD.
I would firstly try borrowing a Windows CD from a friend then using the same CD key on your current installation for the borrowed CD. You can use Magic Jelly Bean Keyfinder (http://magicaljellybean.com/keyfinder/) to get your current CD key.
Else you can use HDClone (http://www.miray.de/download/sat.hdclone.HTML) to duplicate your smaller hdd onto your larger one (assuming that's what you mean by a hard disk upgrade).
Remember to backup before performing any clone operations, even though it is only copying, weirder things have happened during read operations.
no
Of course, backup all your files to an external hard drive and perform a clean install with your Vista disk. They only make it easy to upgrade never downgrade. If you do not have an external hard drive, create a disk partition to use as your file backup.
To install Windows 95 from MS-DOS, run an F disk before formatting the hard disk. Then add a switch /S so that the partition will be bootable.
Yes, you can
You shouldn't lose anything when upgrading to Windows 10. But it is best to backup any important data, files and folders, to an external hard drive, flash drive, CD disk, before beginning the upgrade.
Since I know longer have a windows 95 disk I can't say for sure but I think it is around 50M to at most 100M. If you have the disk package it should say or the upgrade screen will probably tell you if you have enough. This is an old system and there is better stuff out there unless you have an old computer you want for some reason.
it takes 0 Mbs of additional space. all of the information is already on your computer- you merely need to "unlock" it from the kernel that is already installed.
On a Windows 98 system, there is very likely to only be one partition on the disk. The difference between formatting the disk and deleting the partition would thus be a matter of semantics. Either way, all the data on the hard drive would be gone.
AFAIK, you don't, unless you use a CD-key for the full version while installing, however, that's pirating, and you may as well just go all out and download a prirated version of windows pro in that case. Not that i would recommend that.
scan disk>??
No, XP will format the disk if that's needed.
hard disk drives (HDD) store all the data, operating systems (windows,mac etc) and all the files. HDD is the most important drive and there cannot be a PC without it.