Well, I think the first thing to check is heat, those games ran on my computer happily with a 5700 Pro in it, so its not too advanced, although Oblivion wouldnt play very well. This could be to do with an overheating Processor, I dont know if your processor is a 64-bit as the 3200+ run at 2.2 stock, but if it is a 64Bit, its either a Newcastle or a Winchester, it depends on which socket, although the Newcastles are renound for overheating, as they have a high power consumption.
The first thing to check would be to make sure your PC isnt in a confined space, or sat on a radiator or something simple like that! But then open her up, give her a clean out make sure the heatsink hasn't dropped off either GPU or CPU and all the fans are spinning when turned on.
Use a piece of monitoring software such as Speedfan for the processor, and ATiTool for your GPU
If this doesnt help, or the temperatures arent high enough to cause concern, then i would check RAM! That is the other main fault in a system.
Hope this helps