coolcamel, I don't think you have lost any of your HDD capacity.

It depends what you mean by 'Mb' i.e. 1000*1000 or 1024*1024!
HDD manafactures use the first one, whereas your PC uses the second, which is about a 5% difference. Bit dishonest if you ask me

As to splitting your HDD down the middle, what you need to do is to use fdisk.
Delete your existing partions, and recreate them - you'll be able to get a bit more than 9Gb out of both of them.