Replacing/Changing Graphics Card?

OK so I wanna buy a PC..Here are the specs: CPU:Intel Core 2 Duo E6400 2.13 GHZ = 4.26 GHZ ( I think its good, no?) GRAPHICS: INTEGRATED/NOT GOOD/TO BE CHANGED Intel GMA X4500 RAM: 2GB Corsair XMS2 DIMM HARDDRIVE: Seagate Barracuda 320 GB (16 MB Cache) SATAII MOTHERBOARD: P4-P5G41 For Playing these games on LOWEST settings : 1) Rainbow Six: Patriots 2) Arma 2:Free 3) Just Cause 2 4) GTA IV (4) 5) Mafia 2 6) L.A. Noire ------------> MY FAVORITE :D Ok so the question: PART1) I heard its possible, but is it true you can disable the INTEGRATED graphics and add a GRAPHICS CARD with Dedicated Video Memory (VRAM)? PART 2) IF YES, HOW WHAT SHOULD I BUY, WHERE? PART 3) DOES ANYBODY KNOW A WEBSITE OR A MANUAL OR SOMETHING THAT I COULD USE THAT TELLS ME HOW TO BUILD IT IN? (EVEN BETTER, CAN YOU HELP ME YOURSELF?) I know I`m asking a lot and I am not really asking this question to the normal yahoo user, but to the experts who know how to do it and it`s their hobby.. :) I would be VERY thankful if you guys could help...I would`nt say I dont know anything about building it in, I heard first you need to switch the onboard graphics off... ( ALSO, HOW DOES THE COMPUTER WORK WITHOUT THE ONBOARD GRAPHICS?)... The only thing I ever did was put in extra RAM, Clean the PC, and change the ventilator... THANKS :) ALL ANSWERS WELCOME :)