This is a simple timeline for the Star Trek TV shows and movies to help new fans keep the events straight.
Star Trek: Enterprise — 2151-2154
TV (2001-Present)
Star Trek: The Original Series — 2263-2269
TV (1966-1969)
Star Trek: The Motion Picture — 2271
Movie (1979)
Star Trek II: The Wrath of Khan — 2285
Movie (1982)
Star Trek III: The Search For Spock — 2285
Movie (1984)
Star Trek IV: The Voyage Home — 2286 (1986)
Movie (1986)
Star Trek V: The Final Frontier — 2287
Movie (1989)
Star Trek VI: The Undiscovered Country — 2293
Movie (1991)
Star Trek: The Next Generation — 2363-2370
TV (1987-1994)
Star Trek: Deep Space Nine — 2369-2375
TV (1993-1999)
Star Trek VII: Generations — 2371 (2295)
Movie (1994)
Star Trek: Voyager — 2371-2378
TV (1995-2001)
Star Trek VIII: First Contact — 2373 (2063)
Movie (1996)
Star Trek IX: Insurrection — 2375
Movie (1998)
Star Trek X: Nemesis — 2380
Movie (2002)
There are many different timelines available on the web, including this extremely detailed one that includes the animated series, the books, and the comics.