A. Windows 2000 has built in support for themes but has no control panel icon for it. To use themes you need to manually run the themes.exe image which is located in the %windir%\system32 directory.
There are some compatibility issues between Windows 2000 and older themes as themes for use with Windows 2000 must be .theme (in Windows 9x they are .the or .thm) so you will need to rename them.
Also Windows 9x sometimes uses an environment variable, %THEMESDIR% which is not used in Windows 2000 so you may need to manually edit the themes file to correct any problems.