WinXP to Win2K...?

AFAIK you will not be able to install W2k over XP as it is an earlier OS - and, even if you succeeded, you would need to install drivers. Those that you have installed are XP drivers and are installed in XP. Sidenote: - whereas W2k drivers will often work with XP the reverse is not necessarily true.

You will need to reload all your drivers and software, regardless of how you manage to install W2k. Many of the program components are stored in the OS System folders, etc.

 

If you only want win2k, you'd need to start over. If you want to dual boot you can try the following:

How do I install Windows 2000 after I've installed Windows XP?
(without 3rd party software)


This procedure will work for FAT32 and NTFS partitions.



Backup NTLDR and NTDETECT.COM

1) In Windows XP, open Windows Explorer and locate NTLDR and NTDETECT.COM in the root directory of your boot drive. These are usually Hidden files, so you'll have to adjust your Explorer options to show them.
2) Copy these files to a blank, formatted floppy, or other location that will be available after the Win2K install.

Install Windows 2000

1) Boot your computer from the Win2K CD and continue with the installation.
2) Proceed with the install. Install Windows 2000 to a different partition than XP is installed in.
3) Complete the Windows install. Allow the computer to boot into Windows 2000.

Repairing the Windows® XP Boot Loader

When the Windows 2000 installation is done, boot the computer into Windows 2000, not Windows XP.

1) Insert the floppy disk that you used earlier (or access the location you used), to backup NTLDR and NTDETECT.COM
2) Copy NTLDR and NTDETECT.COM back to the root directory of your boot drive. Again, you may have to adjust your Explorer Options.

Now, you'll be able to restart your computer and boot into Win 2K or Win XP. This procedure is necessary because the Win XP version of NTLDR and NTDETECT.COM will boot Windows 2000, but not vice-versa.