Originally Posted by railroadtycoon
Keikyu (Keihin Electric Express Railway Company) trains run to Yokosuka Chuo Station.
Keikyu's main station in Tokyo is Shinagawa Station. Note that Keikyu Express
急行 trains do not stop at Yokosuka Chuo, but all others (limited express, local, rapid etc) do.
If possible take a NEX (Narita Express) to Shinagawa Station instead of Tokyo Station. If you take a NEX to Tokyo, transfer to any JR line down to Shinagawa Station and transfer to Keikyu there.
Off topic, Yokosuka Chuo station is breifly mentioned in this music video about Keikyu lol
http://www.youtube.com/watch?v=-JVJZTRpYxg 
So things have changed on that line. When I lived there (30 years ago), there was:
- kaisoku tokyu (green kanji - fastest)
- can't remember the name (red kanji)
- kakueki teisha (black)
Anyway, is there a place to leave luggage in shinagawa?