I still regularly play MoM, both in DOSBox and on bare metal, and have never really had problems like you describe. The game certainly will run from HDD only - in fact I lost my CD years ago and just copy the files from HDD to HDD.

I'm pretty sure 686 isn't the problem, I've played it on a P3 not too long ago.

583k doesn't sound like a lot though.
- are you using DOS=HIGH,UMB?
- is EMM386.EXE running?
- are you loading all drivers with DEVICEHIGH (in config.sys) or LH (in autoexec.bat)?

Turns out the problem was I had forgotten the "RAM" parameter to EMM386.EXE.
I had:
DEVICE=EMM386.EXE 4096
which gave me 4mb of expanded memory but no upper memory (UMBs).
Changing that line to:
DEVICE=EMM386.EXE 4096 RAM
enabled upper memory which allowed drivers to be loaded high and freed up plenty of conventional memory for the game.

I'd still like to be able to run from just the HD. I tried copying all the files from the CD, but I must not have them arranged correctly, because it still asks for the CD when I try to run the game. How do you have the files/directories arranged so that it doesn't look for the CD?

With my MoM 1.2 CD, I manually copy the 'game' sub-directory to my hard disk and run install.exe from the destination directory to configure sound. The game should run without the CD then.

Thanks, that did the trick.

And just to clarify for any future readers of this thread, you only need to copy the contents of the game directory on the CD. You don't need any of the files at the top level of the CD. Once you've copied the files from the game directory to a directory on your hard drive, switch to that directory and run install .exe.