Hi same_PC_EXP_as_IT_Crowd,
Radeon HD 6870 will be able to fit with your system with PCI Express x 16 slot. However, the minimum system requirements for this card is 500 W which does not met with your system's power supply. Here is the link whih hows the compatible video cards for your system: http://dell.to/SnqCKE
Please reply for any clarifications.