This helped me :
I decided to ditch the batch file which came with the .zip. Apparently mounting in the bat doesnt work, or atleast it causes something to go wrong. Here is what i did to get this to work :
start dosbox
mount a [x:\path here where\your simearth\install files are\located] ex. my line would look like this -> mount a c:\games\old\tmp
a:
install.exe [DONT run the setup.bat]
select drive A: [where you are installing from]
select drive C: [where you are installing to]
after this you can select screen resolutions and sound devices you like the most.
select preferred language
you can check the setup once more before programs copies the files.
press SPACE after copying is done.
once installation is complete, go to your new simearth folder and run simearth.exe.
Enjoy.
I assume reader has allready mounted hes/hers game directory to c: or similiar, so the final path might look somethign like this -> c:\simearth.
The .zip had custom made setup.bat which failed to mount virtual drive. I just manually made A: and then installed from it. Dosbox version 0.74.