As for the hard drive, it may be that some of the data is wasted, or it is being used (sometimes the OEM decide to use it for 'utilities' of some sort).
You can check this out by going to Start > Run... > type 'diskmgmt.msc' (If in Windows Vista, accept the UAC dialog box). Under 'Status', what partitions do you have there? You should have at least a 'Healthy (System)'. State others here...
As for the memory, you could try a program called "MemTest". This can be found here: http://hcidesign.com/memtest/
Download and type the amount of RAM you have installed in your computer, and see what results you get back.