Posted By:
PCYou need to get to Grand Central Station -- apologies if you know where it is, but if you don't, it's at 42nd and Park Avenue. There are entrances on the south side of Grand Central on 42nd and on the east and west sides on 43rd. You can also get in on 45th, through the main entrance to the MetLife Building.
Here's a link to the Metro North schedule, showing times from Grand Central to White Plains (click on "Schedules", then on "Metro North"). You'll have play around with the site to get the date you want, and the return times. Buy a round trip ticket before boarding, which is cheaper than buying it on the train.
http://as0.mta.info/mnr/schedules/sched_results.cfm