The "lag" probably come from the fact your computer is not fast enough. No dice on that one. You might want to make sure that you have the latest version of DOSBox tough: the latest versions are way more efficient as far as speed goes.
To navigate in DOSBox, you need to know the basic DOS commands. Those commands are DIR (to show the files in the directory) and CD (to change directory).
I am guessing that you've set your autoexec in DOSBox configuration file to go straight to MoM directory after mounting the C: drive. If this is indeed the case, and that MoM directory is in the same parent directory than where you place your other DOSBox games, simply type "cd .." to go down one level and type DIR. You should normally see MoM directory and all the other directories and files in the same emplacement.
If it is not the case then you'll need to be more specific on what happen when you boot DOSBox. This is my best guess... But it's only a guess.
To answer your other question... What you do to be able to play Ascendancy is simply to run the right file. Which should normaly be Ascend.exe or Antag.exe. It is possible that you need to set up the sound also, so if sound don't work before starting the game you should run setsound.exe and select soundblaster settings. And, of course, you need to get to the right directory first. Use CD for that.
Don't hesitate to post again if you need more help.
