If you want a conducted tour of the battlefields and landing zones there are several specialist tour companies - Holts Tours is one I know of that has temepted me before, see
http://www.battletours.co.uk/
, but stick battelfield tours into Google and you'll find several.
But if you don't want a guide then its easy-peasy to do it yourself by car, take the ferry to Caen, use the web to prebook some hotels. The war museum in Caen is not to be missed, and the rest of the sites and beach are well signposted. The Holts have also published guide books to the sites - see
http://www.amazon.co.uk/exec/obidos/ASIN/085052662
0/ref=pd_sim_b_dp_1/026-9184632-1316466
so it very easy to do it yourself.