MegaStar reports:

Tom Cruise is rumoured to be making an appearance in the new Star Trek film.
The internet is awash with the story that Lost creator JJ Abrams, who directed Cruise in MI:III – or Milli, as we still like to call it – has asked TC to appear in his forthcoming reinvention of Star Trek.
The suggestion is that Cruise will play Christopher Pike, which will now get all the Trekkies amongst you terribly excited. For those of you with social skills though, Pike was the predecessor to Captain Kirk and is a cult figure in the series.
Unlikely? Well, as Total Film points out, Cruise has done cameos before (such as Goldmember) and the Milli connection could help. Star Trek is slated for a 2008 release…

CanMag has more details on Tom’s role:
Cruise will play the role of Captain Christopher Pike, James T. Kirk’s predecessor as captain of the U.S.S. Enterprise and Mr. Spock’s first commanding officer. Spock supposedly served with Pike for a decade and we encounter there relationship in the two-part series opener, “The Menagerie.”

On Tom as an actor they say this:
“…You have to admit that he would make a great addition as a smaller role. Cruise may have some exploited flaws, but they guy not only knows how to resurrect a studio (*cough* UA), but is a terrific actor.”