While several questions have already been answered about removing an OS from a dual-booting machine, most refer to Windows 7 vs. Linux/Vista/XP.
I have Windows 2000 installed on my older hard drive (Drive C). Later on I bought a new hard drive and installed XP's under Windows 2000 environment. Each time I turned my PC on, I had the choice of Windows 2000 or XP OS, which I still have. I eventually stopped using the Windows 2000 OS and as the older hard drive where this OS is installed is getting old, I plan to remove it completely.
The problem is that the active master boot record is on this very hard drive. So when I remove the hard drive, I get no OS loader, no matter what boot drive I choose in BIOS. Apparently I have to set the boot record on the newer hard drive with XP's.
Some advise to use the bootable XP CD and try to set the active MBR from there.. I don't have the CD anymore. Regardless, I suspect there is much less to solving this problem than running the recovery console, like a simple
boot.ini file edit. But I might be wrong.