"Being new to this" I have to ask you why would you want to do that?
I assume that you have the two drives already installed. To put on both OSes just install windows 98, then once you have that installed, reboot (with the windows XP CD in the CD-rom - so it can boot from it) and installl windows XP.
When going through the windows XP installation be sure to select the other harddrive you want to install it on, or else it will put in on to the one with windows 98.
how can I run windows xp and win98 on the same computer with 2 seprate hardrives? i'm new at this stuff and need it explained in simple terms.
Do you have a version of Windows already installed? If so, which one? There are a variety of "easy" solutions that we can apply here. For example, there's no reason to reinstall Win98 if you already have one in running trim...