Computer Question-- Partitioned Drive

[atomik kinder]

Okay, my computer has a 120Gb hard drive and it is partitioned into 20Gb for the C drive and 100Gb for the D drive. I have also added a 300Gb drive too. Anyway, my question is...can the partition be easily moved without formatting the drive or anything too time consuming like that? I have a Sony Vaio that I use to do a bit of home video transfer and video slide shows for special occasions, mostly for people I know, I have done a few jobs for family and friends of friends and co-workers. The thing is, my 20Gb space is almost completely filled and the DVD authoring program I use, Nero, transfers all of the file to the C drive, so if any files are particularly large, it will fill up my drive. The reason it seems that it is partitioned is because I have the gigapocket recorder on my computer, which I do use to copy the VHS home video tapes and to record TV.
I was thinking maybe I would just install a new, larger hard drive, but I am looking for a quick fix. Also, even though I installed a second drive, I am just worried that if I install a different one, all of my stuff won't work, like the gigapocket.
Any help would be greatly appreciated!

Yes, long winded I know.