Iron Man 2 director, Favreau, confirms that Tony Stark's dear old Dad Howard will play a part in the events of The First Avenger: Captain America..
Asked about Stark senior's possible appearance in Cap..
"Yeah, because he was around then. ['Captain America'] is World War II. It wouldn't be that same actor, probably, because he would be much younger.[Howard Stark] was starting out during that time, and [he] was involved with the war effort, much like Howard Hughes,"
In Iron Man 2, Howard Stark is played by John Slattery, who appears in a video reel flashback scene and plays an important part in unraveling a key plot mystery. How big Stark's part in Captain America will be is unknown, it could be a cameo or a full supporting role. Either way its a nice way to tie the movies together.