I have two internal harddrives in my system, c: with Windows ME, d: blank. Want to install Windows 98 on the d:, but with Windows ME booted, it won't allow the 98 installer to run.

How does one accomplish this?

are you trying to dual boot? or just have abackup drive? are u using 3rd party software?--if you are trying to dual boot i would suggest having both os's on the same drive. there are ways of doing this without third party software but it gets rather complicated --too much to fit here
either way before trying any of this--3rd party or not --backup!

You cannot run two win9x/ME Operating systems on one computer without using a boot manager.

Technically, wes is correct if both operating systems are on the same physical drive or partition.

However in your case, it seems that you could install Win98 on the D: drive. Then, every time you want to switch between OS's, you have to manually go into the BIOS each time and change the boot source order from C: to D: or vice-versa. As you can probably tell, this is not a preferred method as it would get annoying over time. But it should work!

Here's an idia:
1. do a minimal install of mandrake or caldera linux. This will give you a good boot manager
2. fdisk remove linux partions
3. remmove drive c and install 98 on 'second' drive
4. edit boot manager - instrutions show at boot time