Wanna upgrade and put in GRAPHICS CARD on Optiplex 960 F428D DELL MOTHERBOARD

Would like to upgrade my desktop computer so I can game! Would like to take it as far as I can for as cheap as I can. Would like to try and get good products though even though the budget is low! Need Ram and Graphics card... but have no idea what to get... HELP!!!! 

Should i even bother with ram?? can i go up? would it be better to scrap?? 

SPECS:

Operating System

Windows 7 Professional 64-bit SP1

CPU

Intel Core 2 Duo E8400 @ 3.00GHz 43 °C

Wolfdale 45nm Technology

RAM

4.00GB Dual-Channel DDR2 @ 398MHz (6-6-6-18)

Motherboard

Dell Inc. 0F428D (CPU) // ---> (Optiplex 960 F428D)

Graphics

VIZIO VX20L (1024x768@75Hz)

Intel 4 Series Internal Chipset (Dell)

Intel 4 Series Internal Chipset (Dell)

Storage

465GB Western Digital WDC WD5000AAKS-75V0A0 (SATA) 42 °C

Optical Drives

TSSTcorp DVD+-RW TS-H653G

Audio

SoundMAX Integrated Digital High Definition Audio