You will need to replace the powersupply with something with a higher output, the E521 comes with a 305 Watt unit, far too weak to power the HD4890.
A unit from a good maker of 550 Watts with two 6 pin PCI-E power leads will suffice but you may need to go higher wattage to get the dual leads.
Good makers are Antec, Corsair, OCZ, Seasonic and Pc Power and cooling.
Stay well away for cheap, high wattage units, they are cheap for a reason.
Expect to pay 60-80 dollars US excluding rebates.
I'm pretty sure the PSU in the e521 does not HAVE those 2 PCI-e 6-pin connectors. Its only got a 305W PSU, which is probably not gonna cut it for a 4890. You probably need/want to buy a new PSU to replace that, which will have those 2 PCI-E connectors that you need. You'll probably want ~500W PSU of decent quality that has at least 2x 6pin PCI-E connectors.
Oh wow- I totally missed that when I looked at the e521 online- didn't realize they have the MOBO on the opposite side. Why would they do that? doesn't make sense to me... I guess maybe they want people to let THEM do the upgrades and stuff, but still- kinda strange. EDIT: that also sucks for themal reasons adding a hot GPU in there.
flyinfinni - Yep. Upside down. It could also explain why Dell reps kept passing me along and not a one of them could (or would?) answer my question.
Coozie, CT, flyin - Oh man... Sounds waaaay out of my league! I just picked up my new graphics card (post order as I live out in the sticks) and was surprised to see I couldn't put it in. Is Dell known for making monkey-proof machines?
Well, thanks so much for your replies, guys. I'm a noob so I think I'll have to either send the gpu back or break down and fork over the cash for a new computer. (Snow's melting here in Sweden. Maybe I'll find a bag of gold!)
I would imagine you could still do it- replacing the PSU is not hard at all. It might be a little tricky getting the case to fit the dual-slot card, but you should be able to do that as well: looks like there is enough space above the PCI-e slot to make a cutout in the back of the case for the vent of the card, just need a jigsaw or something like that to cut the right size out (I couldn't see anything in the way on the pics). Might be more effort that its worth though and better to just build a new rig. lol- I don't know what to tell you about that... ;-) Good luck