The internal looks similar. But the problem was the PCI-E slot is top one and the USB ports besides it make it impossible to use a double slot card. I actually bought a 5770 and just can't get it to fit.
To be honest, my gaming needs are not real high; most of the time I just play WOW; occasionally, I will play some FPS. 17'' monitor only.
Hi, I have a DELL E520 and I got a Powercolor HD5770 which is a single slot card that fits in very neatly. See http://www.powercolor.com/au/products_features.asp?id=209
for details. The issue with the E520 is that the motherboard is BTX, meaning that all of the expansion cards sit the opposite way up from ATX motherboards, i.e. the HSF faces upwards rather than downwards as in an ATX. That is why only a single slot card will fit as there is no expansion slot above the one PCI-e slot. The HSF on the HD5770 faces upwards and sits quite high but it doesn't interfere with any of the internals in the case. It also means that the fan can clear air well away from the GPU into the case near the rear vents instead of having it trapped between the Graphics card and other PCI expansion cards (in this case my Audigy 2ZS sound card).The performance is more than adequate for my gaming needs (Call of Duty Modern Warfare 2) on a 20" monitor on maximum resolution. Powercolor also make an HD6850 single slot (http://www.powercolor.com/au/products_features.asp?id=342
), which is quite a bit longer but thinner so it should fit in beneath the CPU HSF shroud. Good luck!