Hi, Toby.
Many of us like to dual-boot two copies of WinXP. Then, if we have problems
with our main installation, we can boot into the second copy to fix it.
Also, the second copy makes a handy sandbox to try out new software before
installing it onto our production system.
But, if you want to delete the copy on D:, then boot into the copy on C: and
delete D:\Windows, including all its files and sub-folders. WinXP won't
obey the command to delete its own "boot folder", so if it refuses to remove
D:\Windows, tell it to delete C:\Windows. If this works, you're down to one
copy of WinXP installed.
The better - and more complete - procedure goes like this:
Boot into WinXP. Go to System Properties | Advanced | Startup and Recovery
Settings. At the top of this page is where you set your Default operating
system. Before changing anything, note what this says. Click the drop-down
arrow to see what other choices are available. In most cases like yours,
there are multiple lines that say the same thing: Microsoft Windows XP
Professional. That's because WinXP Setup always uses that phrase; you'll
see later how to edit it so that you can tell which copy of WinXP is which.
Now click the Edit button; this will open C:\boot.ini in Notepad so that you
can read it and edit it. Under [operating systems] you should see at least
one line, probably 2, perhaps more. Each has the form:
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Microsoft Windows XP
Professional" /fastdetect
Although the details might be different on your computer, most likely your
Drive C: will be described as rdisk(0)partition(1); your Drive D: (on the
same physical disk) will be rdisk(0)partition (2). (Physical disks are
numbered starting with zero; partitions are numbered starting with one on
each physical disk.) You can edit the label within the quotation marks to
say "WinXP (C

" and "WinXP (D

", or whatever you like. The computer
ignores them, but your labels will show up on the menu when you reboot.
When you are sure which copy you want to keep, be sure it is selected as the
Default. It will match one of those under [operating systems]; delete the
other one from [operating systems]. Save the new version of boot.ini and OK
your way out. Then delete the boot folder (D:\Windows or C:\Windows) as
explained above to recover the wasted disk space.
You MIGHT want to delete all or parts of the unused \Documents and Settings
and \Program Files folders, too, but do so very cautiously. WinXP can use
multiple such folders, no matter which drive they are on, and you may be
using D:\Program Files from C:\Windows, or vice versa.
RC