if you're running windows vista or 7 you can easily resize partitions into unused space adjacent to said partition without use of 3rd party software.
right click 'computer', select 'manage', click 'disk management', right click in your partition (typically c: drive), select 'extend volume', and follow the prompts (pretty much just click 'next' or 'ok' 3 or 4 times), voila - all 500gb back.
This possible solution sounded so easy that I decided to try it, altho I am using Win XP with SP3. Whaddya know, the same parameters are there and it was a cinch to follow your instructions and creat a new partition. Un-be-bloody-lievable! I just KNEW those 300+ GBs didn't fly off into the ether, and now they are back. Thinking about it, having the second partition may be a more efficient way to manage the HDD anyway. So thank you Brandon. I just LOVE it when people are smarter than I am; that's how I learn stuff.