Using "convert [your drive letter]: /fs:ntfs" will indeed utilize the full disk capacity, but there are a few things to take care of:
1. Before converting, defragment your drive.
2. Don't proceed if you have less than 10% free HD space.
3. The above conversion from commandline amounts by default to 512 bytes clustersize (no other options, sorry...), which should be a handicap for your system. The default for average NTFS partitions is 4KB, which should work fine. You have to use third party software to change your clustersize without formatting (Partition Commander, Partition Magic, Partition Expert... whatever you like, unfortunately none of them has a working demo).
In short, I wouldn't recommend using the above tip, unless you can borrow from a friend of yours a startup diskette/CD for any of the above programs and change the clustersize from 512 bytes to 4 or 8K.
Determining the clustersize is simple: create a very small text file (say 10-11 letters), save it and then rightclick it in Explorer and pick "properties"... The reported "size on disk" should be your current clustersize.