Well, you can try using "TURBOKEY Z4" to slow down key repeating to a crawl...
The game could have been programmed to process keys as soon as they are pressed, yet still have the enemy movement on a selectable delay; but that's not how it is, key processing is also delayed.
If you run the game with a /? parameter, you will find the author's name, email address, and mailing address. There's a request for a donation, so maybe if you're generous you can get the BASIC source code and change it to be the way you want it, or maybe after a dozen years the author will just give you the source simply for caring enough to ask.