It really depends on how big your partition is for 2k. It may not work after the first 6GB of space. Either way, you will have to run Win2k's repair off the CD, so you can boot between both OS's.
Once you get 98 installed, you'll be unable to boot in to 2k. Get the Win2k CD and boot off of that as if you were going to install. Do everything just like you're gonna install 2k, but when you get to the installation screen, there should be an option from there to do so. You will then have two recovery options: console or Win2k CD recovery. If you choose the console, all you need to do is type "fixboot" and hit enter. Choose the other and just have the CD examine the boot sector, which is will repair. Once that's done, you should be good to go.
Usually, it's better for 98 to be on C: and 2k to be on D: