My questions are several. I am not computer literate so bear with me.

I have a new computer, a Dell Inspiron 530s with 4gb Ram, 500gb hard drive but not sufficient graphics to operate my Flight Simulator program.

It says I need a GeForce 9950 GT 1 gb DDR2 PCI-E 2.0 graphics card or better..
1. How much is the card I need and can I install it myself, remember, I am not computer literate.

2. My new computer, only had it two weeks and use it only for very limited uses.
A window comes on that says "running out of space on discovery "D".
2. What does that mean and why should I get that message on a new computer?

Whew! Thanks.

The Inspiron 530S is a slimiline case. There are four expansion slots, all are half height. The specifications on the slots are:
PCI: 2 Slots
PCIe x1: 1 Slot
PCIe x16 (Graphics): 1 Slot

You would need a graphics card of the model you mentioned that is able to fit a PCIe x16 half height slot.

You can install it yourself if you are not bothered by opening the case.