Not everyone is lucky to have 2 or more Operating Systems (OS) - I am.
I have 3 in fact, Windows 98 SE, Millennium (ME) and recently Windows 2000. So, I decided to load at least 2 into my PC for starters.
I also have 2 Hard Disk Drives (HDD), so it was actually very simple for me to install each; Windows ME and Windows 98SE, on separate HDDs without a hitch. You can only install one OS on one HDD while disabling the other - then switch them, to install the other OS.
Now came the interesting part, how to somehow make a selection which system to use at Startup?
Surfing the WWW, I came across a (so far, so good) 'easy to install' and FREE software (aka Boot Manager) that will do all the hard work for you and promptly present you with a dialog box asking you
which system do you want to boot into? message every time you start your computer.
You can even set a default OS to boot when you don't make a choice within 10 seconds (or whichever time you set).
Better yet, if each HDD has partitions themselves, you can select to hide the partitions (and even password it) depending on which OS you booted up with.
I don't know, but I suppose this is to avoid messing around with the system files of Windows 98SE if you have just boot up with Windows ME and vice-versa.
The software I use now can be downloaded for FREE from here. Oh yes, you don't have to stop at using only 2 OSes on your PC using this Boot Manager, you can use 3 or more even.
For more feedback also read the topic at GIDForums™ here on this site.
Why would you need to have 2 OSes on your PC? Well, for me at least, it solved this problem for a while until I learnt that it was NOT actually a problem at all.