Native resolution on new monitor and underpowered video card

HD 5770 should be enough for those game.

If you really, really want lots of eye candy then get the HD 5850.

Wait, you got a Dell 410. How many watts can the power supply provide? You need to look at the sticker.

I recently upgraded my PSU, videocard, and CPU in my XPS 410, and I actually have the old PSU sitting right here... lets see... yeah, its 375W.

From my experience, what you're going to need to do, is buy a new standard ATX sized PSU (I went with a 630W continuous 80 Plus certified model), and turn it upside down when you install. This will allow you to get 2 screws in, one in each corner, which is enough to hold the PSU securely in place... so long as you don't plan to be carting around your PC too much.
-Keep in mind that there will be a very slight gap in the back, since the ATX PSU isn't as fat as the BTX one Dell used. It doesn't seem to matter.

More tips: You're going to want a PSU that has a bit longer power cables, and one with less thick power cables, otherwise wire management is going to be a bit of a nightmare. If you open your case up, you'll see that dell has some of the cables route all around the outside of the MOBO, so try to keep that in mind when you're selecting a PSU, otherwise you're going to have to get creative with zips like I had to...

fulle pretty much addressed this for me but I'll add what I had.

Dell
Model N375P - 00
Ref. No.: NPS-375AB B REV: 02
Input 100 - 120V ~ / 11.4A 50 - 60 Hz
200 - 240V ~ / 6.1A

Output +5V *** / 22.0A, -12V / 1.0A,
+12VA *** / 18.0A, +3.3V / 17.0A,
+12VB *** / 18.0A, + 5VFP / 2.0A,

Max Combined Power On +5 and +3.3V output is 150W

Max Combined Output Current on +12VA & +12VB Output is 30A

+5 & 3.3V 150W. +12VA & +12VB 30A
+5 & 3.3V 150W. +12VA & +12VB 30A

I'd been a little concerned about swapping out the power supply in the case simply because it seems a bit cluttered in there. I know that a lot of the newer cards are going to run hot, though my present 8600 seems to be floating at the 150 fahrenheit mark at idle which seems sort of warm to me, and I'm concerned that there may not be enough airflow to keep things cool.

The 5770 can't do DX11 at 1920 resolution at 30 fps in Dirt2 which has only minor incorporation of DX11 features. I'd therefore make your PSU determination based upon a 58xx series card.

use this to "do the math":

http://www.antec.outervision.com/

@Indecisive_Man

My 5850's temps were fine... even when overclocked to slightly over a 900MHz core 4x1220 memory (gave it a nudge in voltage to get there). The fan's a touch loud when it gets up to 40% or so, but it blows most of the hot air out of the case. It also runs considerably cooler than my 8800 used to (my 8800 would reach over 90C and dump the hot air right into my CPU's heatsink)... with a reasonable fan profile, I can keep the 5850 under 70C without a problem. My CPU temps on the other hand....

That propriety heatsink for the CPU is a POS. Not much I can do though, since you can't replace it.... When I stress test my poor Q6700 in Prime, I can push it up to 72C, despite cleaning up the airflow in the case the best I could, and using expensive thermal grease. Its just one of those things... that's maybe a sort of warm load temp, but still safely within the CPU's limitations...

Anyway, though, I wouldn't worry about the 5850's temps.... its a good card.

Thanks for all the input guys. Much appreciated. I'm thinking about maybe grabbing one of the Corsair power supplies, Corsair 650TX and then look at the video cards. My hope being that if I build out a new system that I can take those two components with me.

Then again, after seeing some images online of builds with the 410 case, perhaps I should just say screw the monitor and wait until I can build the new system. I'd link the pictures but I'm a little foggy on the cross-site linking to some place other than Newegg.