you still havent provided enough info on your current hardware.....
we need to know..
how much you're willing to spend
your psu (power supply unit), make and wattage, motherboard model, RAM, etc..
alternatively if its a prebuilt pc, the model number and the maker eg: HP 1120a...
if you have no clue where to find this info download SIW or Everest home and look it up...
putting a new video card is as simple as 6 steps, provided the motherboard does support a vid card:
-unplug power (mains) and cables.
-open up your pc case, destatic yourself (touch the case frame before you touch anything else)
-find the slot that your vid card goes to, note if you have to push a locking mechanism or not before installing.
-phillips head screwdriver remove the pannel that will be for your new vid card
-install vid card securly, lock if needed and dont forget to screw it in and attach power connector if neccesary.
-close case up, connect all cables etc, go to bios and change a few settings, bootup windows and install drivers.