welcome to tech forums
and as far as the PSU goes, depends on what the wattage/amperage on the PSU is. I'll need a minute to look up the PSU specs. And if tis too low powered to handle the card then you're gonna have to look around for a psu specifically for your computer. It isn't a standard ATX Power Supply so you can't get just any psu. you might have to order one straight from dell.
if you could possibly open up the computer and see what the wattage is on the PSU that would give us a good idea of if you can run the 8600 on it. From what i've seen it has a 300w psu, but that could be wrong.