Urk.

Whichever way you dice it, this is going to be messy.

The flat-out easiest way of doing this is to use partitionmagic or similar to resize the volumes.

If you convert the disk to a dynamic disk, you'll have unlimited partitions and the disk will not be readable by any other operating system, no sirree. Apart from Linux, but that's just a viral cancer spreading across the face of computing, so that doesn't count.

I don't think, however, that you can merge volumes. You may be able to resize a volume down (i.e. the data volume) and then expand the system volume into the free space.