Upgrading my emachines T2385 HELP!!!

[noob/wit/comps]

I need input on how to upgrade my Emachines T2385, i have around $200 to upgrade. My goal is to be able to have a computer to be able to play oblivion. Here are my specs:
512 ram with one other slot open
2.3 ghz intel celeron processor
80gb hard drive
16x dvd drive
3d intel extreme graphics video card(integrated i think)

I dont have any AGP or PCIe slots, have 2 free PCI slots open though. Please help out I'm obviously not great with computers

 

[tweaker]

You might as well do a complete rebuild as you lack both AGP & PCIe slots. Your machine is also quite weak in the CPU/RAM department. Oblivion is extremely demanding.

~$200 isnt nearly enough for all this, to be honest. First save up some more money, then sell your old computer and build a new one.