Heh, sorry, I noticed this "a bit" late
Anyway, a few ways exist to get in there. Either contact a travel agency in Ukraine, they organize one day trips to the Chernobyl zone. They are pretty expensive, tho..
The better way is to contact organization called Chernobyl Interinform. It's some kind of unit of Ukrainian goverment, in charge of giving information of the exclusion zone, cleaning it etc. I don't have the contact information available here, but Google probably helps..