Starship Troopers is a book by Robert A. Heinlein, published in 1959.
Starship Troopers is also a 1997 movie directed by Paul Verhoeven. Allegedly it's based on the book. In practice, aside from the title and a few minor setting elements that are more flavor than plot-crucial, it has nothing in common.
Starcraft is a real-time strategy computer game. Rumor has it that it was inspired by the book. It has the same sort of gritty realism feel as the book does. It has humans in it (also called Terrans), some of whom are telepaths. It has a race of bugs (Zerg) that sort of resemble the book's Arachnids. It also has a third race (Protoss) that could conceivably be the same ones inhabiting that alien city that the book's protagonist was assaulting in the opening chapter (if one squints at it just right and doesn't think too hard about it). Beyond that, however, the storyline and characters are completely different.
I watched the movie because it was a sci-fi movie. I played the game because an ex-SO insisted I'd like it, and then when my brother found out, he dragged me into his online community. Personal history ensued... I read the book because of the game. I like all three. It probably helps to think of them all as separate entities, but I enjoy comparing the book to the game, as it adds to my appreciation of both.
Starcraft also has its own line of books, at least two of which are novelizations of the game's plotline (Liberty's Crusade by Jeff Grubb covers the first set of Terran missions, Queen of Blades by Aaron Rosenberg does likewise for the first Zerg missions) and one is a prequel (Uprising by Micky Neilson - released as an ebook only, swaddled in anticopy tech, no longer being sold by Amazon, may be impossible to find, was a damn good book). They've been putting out others as well, continuing to expand the universe in new directions; Speed of Darkness by Tracy Hickman is totally awesome, Shadow of the Xel'Naga by Gabriel Mesta totally sucked.
Star Trek was my main obsession all through my youth, resulting in a fairly sizeable collection of books (mostly TOS). No money was safe in my hands back in those days because I would use it to buy books instead of lunch/bus tickets/save for emergencies.
Stargate is my current biggest sci-fi obsession; I jumped to it as the Star Trek franchise went stale and sank. SG1 has since gone stale and sunk as well, though Atlantis is still decent.
Star Wars I-III is an epic story about the fall of a man who sacrificed himself out of love for his wife - only to find that in so doing, he lost her. Unfortunately, it was badly written and executed, so nobody noticed. IV-VI would probably have been about his redemption had I-III been filmed first, but they stand alone as their own complete story pretty well.
I think that's everything that has ever passed through my sci-fi life that starts with "Star."