I know absolutely nothing about graphics card and cpu upgrading.. So it will be great if someone can enlighten me about this graphics card. Will it burn my motherboard, will it consume tonnes of power, or can my computer even use this thing due to space constrains or incorrect plug present.
Well it should be a little more expensive, but the HD 5670 is using 40nm tech (8800GT aka G92 is 65nm), uses a lot less power and exhausts lot less heat. They're abuot the same performance. Plus i think that the 8800GT would cause problems 'cause of the PSU.
Not according to the required specs I quoted from the link you provided, you're not making your statement on facts, you're making it on your assumption!
Dell doesn't put power supplies in their computers with a lot of upgrade headroom, they install power supplies that serious upgrading requires the customer to have to also upgrade the power supply, that's basically Dell's sales policy, to keep customers at their mercy.
The OP can follow your recommendation for the 5670, but he will also end up getting a higher performing power supply, low powering a GPU and load stressing a power supply can eventually lead to serious problems.
^ That does not change XFX requirements, and if the 5670 draws a solid 100w load all by itself, that is why XFX recommends a minimum 400W power supply, what about that requirement, don't you understand?