No, you do not need shots to travel to Poland. I know when I studied abroad (studied in Austria, but travelled all over Europe) in the mid 70's we had to get shots before we left, but not any more. Although my husband was born in France, he is 100% Polish and just a year ago this week we went to visit our son who was studying abroad and took a train from Salzbug to Warsaw- loved it!
Jenn, the CDC website reccomends you be current on your routine vaccinations = MMR,Td and Polio (depending on your age, an adult Polio booster may be given). Also they reccomend having the Hepatitis A & B (which you may have already had) and getting the Typhoid vaccination. It's good to be protected just in case.