I'm looking to upgrade my PC. and I have no idea where would be the best and cheapest place to start.

Specs: Dell XPS 400

• Processor: Intel(R) Pentium(R) D CPU 2.80GHz (2 CPUs)
  
• Memory: 3070MB RAM
  
• Hard Drive: 249 GB + 500 GB External Hard Drive
  
• Video Card: NVIDIA GeForce 7300 LE
•  Monitor: Plug and Play Monitor
  
• Sound Card: SigmaTel Audio
  
• Speakers/Headphones: Audio FX pro 5+1
•  Keyboard: Logitech G15 gaming Keyboard
  
• Mouse: Logitech USB MX518 Optical Mouse
  

• Operating System: Windows 7 32-bit
• EDIT: My motherboard is Dell Inc. 0FJ030 
  

I have the same computer for the most part (Didn't add any RAM or upgrade to Windows 7), but this graphics card I got today helped me go from barely being able to run Street Fighter IV, to running it pretty well. I'm sure you can find a better video card for a better deal, I'm just waiting for the PC brigade to respond.

I dunno If i'm going to be able to help but if you posted some of the games you're looking to play and a budget it might get you some results.  Knowing the motherboard would also be useful if you have that on hand.

That computer doesn't need an upgrade as much as it needs a complete overhaul. 

If you still want to upgrade the pc, so you can get a bit more life out of it without buying or building a new pc, the you need a bigger powerwatt supply and a new videocard.

Yeah get a 8800gt / 9800 gt for cheap and you should get respectable performance in most games.