I'm not a video card guru because I don't game. I can tell you that Sapphire is a good brand name.
Video cards are typically categorized by the processor on the card--the one you chose uses a Radeon 5750. I'd suggest you do a separate post in the gaming area regarding video. Tell them your budget.
That's assuming you are a gamer. If not, you certainly don't need a Radeon 5750.
Re the Corsair supply. Probably a good choice and probably made by Seasonic. Personally, I would go with a known Seasonic such as: Newegg.com - SeaSonic S12II 520 Bronze 520W ATX12V V2.3 / EPS 12V V2.91 80 PLUS BRONZE Certified Active PFC Power Supply Newegg.com - SeaSonic M12II 520 Bronze 520W ATX12V V2.3 / EPS 12V V2.91 SLI Ready 80 PLUS BRONZE Certified Modular Active PFC Power Supply Newegg.com - SeaSonic S12II 620 Bronze 620W ATX12V V2.3 / EPS 12V V2.91 80 PLUS BRONZE Certified Active PFC Power Supply
All 70 to 80 bucks and 520 to 630 Watts. The middle one, with the M in the model number, is a modular unit. The unneeded cables are detachable, which makes for a cleaner install and less clutter. Generally worthwhile.
Go to Crucial.com. Enter your Dell model number in the configurator. It will spit out the exact model numbers of Crucial brand RAM that is guaranteed to be compatible with your specific Dell.
You can then buy the RAM direct from Crucial or go back to Newegg and price it there.
You may well be able to get away with PNY, but RAM is so finicky that I won't vary from Crucial or Corsair. It's up to you to CONFIRM that any chosen RAM is in fact compatible with your Dell motherboard. Look at your owner's manual, etc.
And you still need confirmation that your Dell can accept a standard ATX power supply. As I said earlier, maybe it will and maybe it won't. It will "fit", but it may not have correct connectors. Dell's used to be non-standard in that respect.
Saw a mention at Tom's Hardware that ATI wants you to have 450 watts if you are running a 5750 video card. Of course, that's not for the card alone. From what I can tell, the card itself maxes out under 100 watts.