The installer is likely misinterpreting your 400 GB of free space, since that is much, much larger than the hard drives available at the time it was written.

As per the DOSBox readme, you can use the "freesize" parameter to set the reported free size of your hard disk when you mount a folder.

I looked up the command you mentioned, but I'm still unsure if that does anything. I typed a number I thought appropriate (5000mb) in when I mounted the C drive. Only when I went to install the game by mounting my CD drive, the same error came up. What am I missing?

Try something more realistic like 500mb to 1gb

So does it go something like mount c c:\ -freesize size 500-1000 mb? I'm not quite understanding.

Judging from your silence, I tried that and now I'm told I have 0 K of free space left. Strange....

Edit: Can someone still help me?

Did you even bother looking at the readme!?

Advanced MOUNT examples (Windows):

4. To mount a hard disk drive with ~870 mb free diskspace (simple version):
mount c d:\dosgames -freesize 870

I did, but I was looking under the command parameters section, which I now realize I totally misunderstood(only putting in kb if you're doing a floppy drive) and not the mount examples. But I know that much more now just how fundamental mounting is to making DosBox work.

Anyways, thanks. Game installed just fine and is running great, apart from some hiccups when cutscenes involving ships change. But I don't think adjusting the speed would matter.