If your hard drive is SATA you might have a problem. Windows 98 , like XP does not have SATA drivers included with the install disc so you would need to find drivers for your hard drive on the internet that work with windows 98 which would be difficult if its a newer hard drive. And if you find the driver you would need to somehow integrate it into the 98 disc ( i know you can do this for XP but not sure about 98) or put them on a floppy disk which may or may not be feasible for you.
Anyways to get to regedit all you do is type regedit in run (Start > Run).
Once you install a second operating system a boot menu should be installed to let you choose between multiple operating systems at startup.
Also I would recommend using linux instead of windows xp or windows 98 because its actually easier than both of those options and may be more likely to work depending on your hardware.
The guide for DC-PC server on linux is here:
http://www.ryochan7.com/blog/2009/07/11 ... iguration/
It works well on ubuntu 8.10 which can be obtained for free from here:
http://old-releases.ubuntu.com/releases/intrepid/
