You need to realize that your hdd will never be nearly as fast as your ram, so while in critical situations(running many many programs.) you will see a small difference, but in basic task you will rarily see an improvement.
No...
You can expand your paging file, but 3GB isn't a low amount, you probably don't need it; most likely it won't even help, and it'll take up space.
RAM is RAM, HDD's are HDD's.