Changing Default Options in Windows 98 & 2000

I’m installing Windows 2000 on a friends computer and I would like to know change the default options in regards to saving stuff in case I have to reinstall the OP again:
I would like to know how to change the default saving options from C:\My Documents to D:\My Documents.
Also, how (if it is possible) can one change the default option to have C:\Documents and Settings\Desktop to D:\Documents and Settings\all users\Desktop?

Thanks in advance.