Re: graphics card wont fit
First and foremost, how old is this PC? Do you still have any sort of warranty on it? If you do and you make any alterations to it, it will void all warranties.
If you don't have any warranties than please list the specs of your PC. That model of Dell probably has numerous variations to choose from. The link you provided doesn't specify what your PC has. If you can list this, it will make it easier for us to recommend parts for you.
Also note: You would have to purchase a new motherboard, case and possibly power supply. The operating system that came with your Dell will not work with the new hardware. So you'll have to acquire an operating system also.
This build would require you to format your current HDD and reinstall windows and all new drivers fresh. You'll have to back-up everything you want to save. You'll basically be rebuilding a computer.
You will be able to use, "Hard drives, Optical Drives, Ram, Processor, sound card and other input devices."