I'm a fan of partitioning for the reasons above and others. If you want to do it and you don't want to lose any info you have already stored then you will need a 3rd party partitioning programme somether like Partition magic. I don't believe there is any other way of partitioning and keeping your data.
I think the ony real advantage of partitioning a drive is that if Windows gets irrepairably corrupted, you can reformat the partition with Windows on it and not lose any data. I keep all my data on a separate partition and this has saved me a couple of times.
Having other partitions also helps avoid some errors with dv editing and rendering etc. I'm not too sure of the technicalities but it's even better to have at least 2 hd's for this purpose so you have two hd's working instead of just one. Plus there's the storage issue. Once you get hooked dv takes up a lot of space.
I used Partition Magic to partition my hard drive from C: to C: and D: It left my original data intact.
I image my C: partition to a second internal IDE drive now and again for an emergency situation.
After imaging, the second hard drive is switched off using a 2 pole key switch. The switch interrupts the yellow 12V and red 5V psu supply to the drive.
Another advantage of partitioning a drive, is that one can selectively defrag each partition only as required thereby speeding up the process.
Most off the shelf computers with reinstallation discs, make use of a separate partition. This is used by the restore disc to restore the computer with the original software installed at the time of purchase. The trouble here, is that any new drivers or software is lost. This is where backing up (copying) this data to a CD is a valuable exercise.
Partitioning in modern comoputers is a waste of time with no real benefits. Buy an external HD and back up to that. You can also lug it around with you and plug into most computers. You will thank me for this one day ;-)0