I have that, but I've put off reading it because I've never read the two Star Trek/X-Men comic books. Does the novel acknowledge them, or is it a totally separate take?
Planet X is loosely a direct sequel to the TNG/X-Men crossover
Second Contact, in that it features the same team of X-Men having a second encounter with the E-E crew, although for the X-Men it's immediately after the end of the comic while for the TNG cast it's a year or two later. Still, the specifics of the comic's story don't come into play; all you need to know is that these particular X-Men have met Picard and crew once before. Which is no worse than, say, "Coming of Age" establishing that Picard and Admiral Quinn knew each other before. You don't need to have seen their earlier meeting to follow this new story.
Everything that Christopher says is true
Fer. The TOS/X-Men crossover comic is indirectly mentioned in the TNG/X-Men comic but I haven't seen a reference to it in the novel, yet. There's a bit of backmatter in the TNG/X-Men comic that says the novel was written with a prologue comic series in mind, but that the comic only came to fruition just 2 months before it came out! Which was just a month ahead of the book. So it seems Marvel/Paramount knew they wanted to do one, but wanted the book done before writing it, and Michael Jan Friedman put some vague references to the comic in it, but nothing concrete. (In the comic they're given wrist devices that are called one thing in the comic and another thing in the novel!) So, as Chris says, I think you can just read
Planet X with little to no problems. I will say that getting
Second Contact was quite expensive for a 14 year old tie-in comic.