Generally speaking, no. Most applications write their settings to the Windows registry. When the installation of Windows they were installed in isn't running, the applications cannot read their important settings, and so most will not function. "Portable" apps that store their setting in a local configuration file should run fine.
Yes.
Yes.
The XP setup program is a 32 bit program, while the 2000 setup program is a 16 bit program.
Windows 2000 applications and settings are kept and Windows XP upgrade is quicker than a fresh new installation of XP.
If there is space left, you can use Partition Magic to reduce the 2000 partition and make room for the 98 partition. Just install into the unpartitioned space. To do a dual boot between the two, the easiest way is to use a program called Wingrub. The address is: https://sourceforge.net/projects/grub4dos . There are examples in the Wingrub program on how to set it up. The documentation examples say it can't be done, but it can. I did it and it works fine.
winnt.exe and winnt32.exe
0ne million two hundred 54 thousand
Yes. Check out these two policy settings: User Configuration | Administrative Templates | Windows Components | Windows Explorer | Hide these specified drives in My Computer And User Configuration | Administrative Templates | Windows Components | Windows Explorer | Prevent access to drives from My Computer
Windows NT/2000 Regedit.exe and Regedt32.exe have two different functions. Windows XP has only one single registry editor.
Yes. There is a process called Dual Booting, but it requires two hard drives. Just search for "how to dual boot windows vista and windows XP?".
command prompt and control panel
No, they are two different programs