You have perhaps the best source for information alive.I highly suggest you sit down and do an interview with your grandfather.And I suggest sooner rather than later.I personally regret not talking with my grandparents about their ancestors when they were still with me.
When you do the interview, try setting up a videocamera to record your Grandpa talking.It will help you keep the facts straight when you start organizing the info.It will also make a priceless family treasure when your grandchildren are asking about their family.
As you ask questions, start with questions about his childhood with as many places, dates and names as possible.Then start asking him about his parents and brothers & sisters.And while you are at it, perhaps any info on your grandmother's side of the family that he might recall.
Go beyond just what their full names were.Try to get him to remember birthplaces and interesting info about them such as occupations, military service and whomever they married.While it might be tough for your grandfather to remember all the details, just encourage him by saying anything he gives you is great help.
Then work your way back with any info he might know about his grandparents or even great grandparents.You might be shocked to learn all the details he might remeber.Longterm memory is generally surprisingly strong even as our overall memory begins to slide.
Good luck, Justin.If you do as I suggested you will have a wealth of information that will prepare you to search even deeper in your family tree.