I'm not exatly sure what you are asking, but:
-by ddr2 or ddr3 graphics card I assume you mean a video card that uses ddr2 or ddr3 memory. Since you have an AGP slot, I don't think you will be able to connect any modern video cards. You need a PCI express slot to use modern video cards. Also, your PSU is really bad, and would probably not be able to power a new card anyway.
-I'm currently writing this on a school computer that is from the same line as your machine (its an optiplex 280). Based on the size of the case and how slow this machine is, I would recommend you save up money to buy a new computer, since a new video card will probably not fit in this case.