It's not that hard, if there's an existing copy of Windows it will just install to another location.
It's been a long time since I used 2000 (actually, it was in the year 2000 I stopped using it. hehe) but if it's anything like XP, there's a boot manager menu you can delve into. I don't have a 2000 system running so I can't tell you exactly how to get there. Open up the control panel, and under System, Advanced, Startup and Recovery, there ought to be a section about what operating systems you can boot. WIth a little digging, you can figure out where each option is, and once you do, you can delete the correct one. Let me know if you need additional help, I'll do some digging.