My guess is you'll not be able to without going back into bootcamp and reformatting your windows partition. I've formatted my own Windows partition as FAT32 for just this reason.
Since you have a lot of data on your NTFS partition, do you have an external HDD and/or enough space on your OS X partition to back up all the important files? You CAN still read the NTFS partion from OS X, just not write to it.
The other option would be to get a 3rd party program that will allow you to see your drives from either operating system. As I said, I used FAT32 so I can read and write to my Windows partition from OS X without issue. I purchased MacDrive 6 from
Mediafour to allow me to view and write to my OS X partition from Windows. So far it's worked great, and is well worth the $50 for the enhanced interoperability.