I can tell that you can do this if you are going to truncate the partition at the end, meaning your root partition is allocated to higher sector addresses than the TrueCrypt partition.
Otherwise there might be a way, but I have no experience with that, yet.
For the former case, proceed like this:
- mount the volume using TrueCrypt to slot 1
- ummount the filesystem from the truecrypt device:
sudo umount /dev/mapper/truecrypt1
- use ntfsresize to shrink the filesystem:
sudo ntfsresize -s <whatever size> /dev/mapper/truecrypt1
- check the filesystem wihtin the mounted volume using
- truncate the partition at the end using
parted (delete the old partition and create a new partition stating at the same start sector as the old one and which is big enough to hold the shrunken file system)
- use a modified version of extcv in Windows to update the TrueCrypt volume headers and adjust the filesystem to the new boundary
Anyways you should check out a more detailed guide on this so you understand what you are doing. However, this procedure requires some knowledge and experience with handling partitions.