Make sure you've defragged to the maximum extent before shrinking but unfortunately, Vista doesn't give you any user control.
You could try shrinking, moving all your user data, special files, email, page file, etc, then shrinking again and adding any further gains to your new partition.
Vista can be picky when it comes to letting you shrink/extend partitions like you want to, especially if they are involving system partitions or partitions its OS are running off of.
If you're lucky, Vista well let you continue to shrink the volume (Only a certain amount at a time) by selecting the shrink volume option after having taken some space from the partition already. You could also try booting from a Vista DVD and using the partitioning screen there to shrink it. There is no need to re-install Vista, though you may consider it if it doesn't let you shrink the volume anymore. 40GB or so is about all you need for Vista, so if you choose to re-install, don't forget to copy your data to the new data partition. You should delete the Vista partition, but keep the data partition you already have. You should be able to use the disk's remaning space later to extend the data partition.
Well, I can't blame you for not knowing, using Disk Director in all, but yes. You may not see it when you first look at the partitioning screen, but there is an advanced options link that'll provide you with it. Even if that option didn't exist, you could still use the command-line in the recovery enviornment and diskpart to accomplish it. MS added extend and shrink commands to diskpart to make that possible.