Right click My Computer icon, Properties, Advanced tab, Startup and Recovery.
In the box for default operating system, click the drop down list and select "Windows 2000 Professional" /fastdetect (if not already chosen). Click OK, OK.
Double click your C drive using My Computer or Windows Explorer. Look for a file called boot.ini under C. If you don't see it, click Tools, Folder Options, View tab. Tick "Show hidden files and folders". Untick "Hide file extensions for known file types". Untick "Hide protected operating system files". Confirm the change. Then click OK.
You should now see the file C:\boot.ini Double click boot.ini which should open in Notepad (or right click and select Open with Notepad).
Under [operating systems], delete the line which reads:
C:\$WIN_NT$.~BT\BOOTSECT.DAT="Microsoft Windows 2000 Professional Setup"
That's the only change you need to make.
Your boot.ini should now read:
multi(0)disk(0)rdisk(0)partition(1)\WINNT="Microsoft Windows 2000 Professional" /fastdetect
This assumes your working copy of Windows 2000 is installed on the primary IDE hard disk, first partition, in the WINNT folder (normally the case). The timeout value is irrelevant when you only have one OS.
Save the changes to boot.ini and exit Notepad.
Restart the computer. You should go straight into Windows 2000 without the dual boot selection menu.
Windows 2000 Setup will have copied an installation folder on to the C drive. The folder is called $WIN_NT$.~BT
Delete the folder to reclaim hard disk space.