I'm going buy EVGA GeForce GT 520 2048 MB DDR3 PCI Express 2.0 DVI/HDMI/VGA Graphics Card, 02G-P3-1529-KR
So my computer will let it use?
That purely depends on your motherboard. If its AGP slot than no. It wont work.
If however, you have PCI express slot than you're golden and your 980w PSU is about 50x overqualified to power it.
There is a good chance that you'll have to remove your current GPU to see what graphics slot you're using. http://img.tomshardware.com/de/2004/12/01/grafikkarten_die_grosse_thg_kaufberatung/pic-agp-pcie-cards.jpg
However, if you download and run GPUz (http://www.techpowerup.com/gpuz/)
it will show you if you have AGP or PCIE card.
Here is how and where GPUz will tell you if you have PCIE slot(that you MUST have to use suggested card)- http://tinyurl.com/pciegpuz
If it says AGP, than you're out of luck and need to find a good AGP card. Used cards are likely your only real option to get a decent AGP card.
On another hand, It might be a good time to upgrade your system, and your PSU is surely ready