Use Partition Magic software, this is a program you can use to make partitions without reinstalling everything, you can do what you wan. for me the best option is 10-30.

About the DVD drive letter, do not worry Partiton Magic performs a rutine to update the windows registry to replace all the references to the old drive letter and replaces with the newone.

Be careful though, because theres is a little possibility that running this software could ruin all the data in your hard drive. It's never happend to me, but there is always a "might be"