You'll be unable to simply add a card to a laptop, you'll need to find one that already has it as an option. But unless you get something high end like the new Asus Gaming laptops you're going to spend alot.
5 Years ago i got a Lenovo Thinkpad T61 with nVidia NVS 140. Cost 1001$ after all the sales & coupons I cound find. Plays up to Starcraft 2 with little issue and ALOT of heat.
As you have little knowledge of computers i would suggest a Dell with plenty of warranty coverage. The Inspiron 15R should suit your needs.
2nd Generation Intel® Core™ i5-2450M processor (2.50 GHz with Turbo Boost 2.0 up to 3.10 GHz)
6GB Dual Channel DDR3 1333MHz
750GB 5400 RPM SATA Hard Drive
AMD Radeon™ HD 6470M (64-bit) 512MB (Dual)
8X Tray Load CD/DVD Burner (Dual Layer DVD+/-R Drive)
15.6" High Definition (720p) LED Display with Truelife™
6-cell (48WHr) Battery
Intel® Centrino® Wireless-N 1030 & Bluetooth
HD Audio 2.0 Support SRS™ Premium Sound
Integrated 10/100 Network Card
Integrated 1.0MP Widescreen HD Webcam