I am heading to NY in a couple of weeks and on our first day there we are heading on a 2 hour cruise with Circle Line around lower manhattan. I would like to stop by Grand Central Station before. Does any one recommend a place for lunch at Grand Central(what about oyster bar) and then from there we are taking the cruise. How should we get from Grand Central to Pier 83?

The Oyster Bar is very good. In addition, there are a flock of new restaurants on the lower level of Grand Central.
If Pier 83 is where the Circle Line Cruise leaves from, then it's at the end of 42nd Street at the Hudson River. You can walk west on 42nd Street from Grand Central. It's about 3/4 of a mile or you can take the #42 bus heading west. Make sure you have the exact change ($1.50) before boarding the bus.

Take the M42 Crosstown bus, westbound, to 12th Avenue (last stop). Bus lets you off at the pier. $1.50 a person in exact change for the bus or purchase a Metro card at the entrance to the subway located in the terminal. Option would be a taxi. Cost would be around $5 not including a tip.

Personally, I find the Oyster Bar horrifically overpriced for what it is - although I do like having beers and oysters in the bar after work. Salmon for lunch at $27? Even the soft shell crab sandwich is in the same price range. And the food ain't THAT great. I would venture down to the food court or to the Grand Central food hall/market on the Lexington Avenue side, where you could assemble a picnic to bring on the cruise: Cheese, bread, etc. from some fine local places. I used to work a few blocks from Grand Central and frequented the food court for lunch - some good vendors down there. As the Oyster Bar is my father's favorite lunch spot in NYC - in the world, probably - I've also eaten there my fair share.