There are many options in running a campaign set in the Starcraft universe. A campaign could recreate the events from Starcraft and Starcraft: Brood Wars games, it could recreate the events from the Starcraft novels, or it could just be set in the same universe, but be a completely new story, as Palladium Books loves to say, the options are limitless.
This conversion of Starcraft is based in an M.D.C. world and is based on the rules presented in the Rifts, but the power levels are very similar to those presented in Phase World and could be unbalancing if brought to Rifts Earth without any modifications. Protoss technology is the most advanced and fits into Phase World the easiest. The technology of the Humans is closer to the orbital communities around Rifts Earth then to Phase World, but it still may be too much for Rifts Earth. The Zerg Swarm do not use technology and because of their nature, they can be easily made to suit Rifts Earth by changing the number Zerg creatures a party has to face at a single time. Most of the Zerg creatures are relatively mindless creatures that are not suitable for player characters, and the few intelligent Zerg creatures are the Cerebrates and they can control thousands of individual Zerg creatures, also not suited for a player character, so the Zerg Swarm should always be kept as an enemy force or at the very least, non-player characters.
There are many different campaigns that could revolve around the Protoss. The universe that Blizzard Entertainment created is very rich and the campaign possibilities are endless. Given that, there are two main ideas that I believe worked the best. The first is replaying the Protoss parts of the computer games, with the player characters playing an increasingly important part of the action. I would not recommend that the players begin the campaign as the Executor that replaces Tassadar, as this effectively gives them control of a large army, but they could easily be part of this army or even an elite force within that army. The end of such a campaign could either be the successful evacuation from the doomed world of Aiur or maybe the players could save it after Tassadar sacrificed himself to destroy the Overmind.
An alternative to playing the story from the game would be to place the players on one of the many colony worlds spread throughout the megaverse. The players could be caught in the immediate aftermath of the invasion with the sudden cutoff of all contact with Aiur and any resources needed from that planet. The players could be involved in helping their colony struggle to survive completely cutoff and in desperate need of supplies. For this idea, I created the Protoss Enclave, a small but powerful group of Protoss colonies located in the Three Galaxies.
While there are many areas for adventure with the Protoss, the ideas for the Humans are just as vast. Of course, there is always the possibility of playing the story from the game, except for the Humans it is much more complicated then for the Protoss. With the Protoss, the computer game focuses on a single Executor put in command to replace Executor Tassadar, but the Humans have four different major Human groups working simultaneously. Each of these groups provides ample opportunities for a campaign.
The first important group is the Terran Confederacy itself. This group is the dominant Human power in the sector and has a large military presence. The players could easily be part of any of the military groups as ground soldiers, fighter pilots, or even as one of the mysterious ghosts. An adventure for this group could follow the story from the first game as part of Alpha Squad that responds to the alien troubles on Mars Sara. The Terran Confederacy collapsed at the end of Starcraft, so afterwards the players could join the Terran Confederacy or become pirates or even join James Raynor and his group.
The second important group is an organization known as the Sons of Korhal. The players could be members of the organization with any position that the Game Master feel appropriate, from lowly soldiers to part of the command group. The Sons of Korhal eventually become the Terran Dominion, which replaces the Terran Confederacy, so after their rise to power, the players could become involved in securing the power of Emperor Arcturas Mensk or part of the military forces that opposes the sudden invasion from Earth. Most of the story line from Starcraft follows this group, so a campaign could easily this.
The third important group is from Earth and its sudden appearance in Starcraft: Brood Wars causes massive changes in that part of the galaxy. The Earth Defense Directorate, as the military group is known, is another opportunity for players to be soldiers or direct other soldiers in military operations with large battles, both on planets and in space. This campaign could easily follow the main Human story line from the Starcraft expansion.
The forth important group is controlled by James Raynor, a former ranger from Mars Sara. Disgusted by the attitude of the Terran Confederacy in the early part of Starcraft, Raynor joins forces with the colonial administrator of Mars Sara (controlled by the game player), and the two become allies with Arcturas Mensk in his quest to overthrow the Terran Confederacy. Unfortunately, Raynor finds that he doesn't like the new system that Mensk is establishing, so he and the former colonial administrator leave with a number of troops and ships. Raynor and his troops are taken to Aiur by Tassadar and help during the final confrontation against the Overmind and also remain behind on Aiur to guard the evacuation of the planet. Raynor and his forces are the only Humans that are considered allies of the Protoss, or at least some of Protoss, and he continues to fight by their side during the Starcraft expansion. A story involving Raynor's group allows the players to fight with the most honorable and decent group of Humans and can lead to some very interesting adventures.