Boot into Windows 98 and put the 2000 disk in - choose
upgrade. It should install the 2000 OS into what is
presently the folder that contains the 98 OS files
(probably the "windows" folder - unless you called it
something else)
If you already tried this and it failed, what was the
error message? - and are C: and D: two different drives
or 2 partitions on the same drive?
Also, why do you want to dual boot 2000 and XP Pro? Is it
so you can play with both? If so then wipe out the 98
from the system and start fresh. Upgrades from 98 like
this "can be" problematic...the machine will run better
with a clean install.(just a thought)
Cheers