Hi!
The first question is easily answered: you need a playable installation of Dark Omen regardless of form (original CD, copy or rip), and then you apply our unofficial mods on your game installation.
I take it that in your second question you're asking about if there are any other games, before or after Dark Omen, that offers a similar game experience? Unfortunately, only a very few. The Myth games, especially the first three games, are somewhat similar. The game "Nexus: The Jupiter Incident" is a sci-fi spaceship battle game that plays somewhat similarly. And of course you should give the battles of the Total War games a try.
Anyone else with some suggestions about RTT games that a Dark Omen veteran must play?