Check the actual case itself as a lot of the Dell computers were designed as being uATX, (Micro ATX form factor). You will definitely need a new PSU as the one supplied by Dell isn't a standard ATX power supply. (This is true for all of the PSU's that dell have.)
You'll need to make sure your case can handle the dimesions for a standard ATX form factor PSU and Motherboard.
I recommend you get a Antec Truepower Power supply probably a 450 watt.
And Get a different motherboard, Asrock aren't great builds. Look at getting a DFI, everybody raves about them. I'd buy one but there not cheap in Australia so i got a gigabyte.( Blood good though.)
Check this mobo.http://www.newegg.com/Product/Produc...82E16813136163
Just check your case dimesions as that will be a silly thing to go buy that gear and realise your case is about a inch or so to small to fit stuff in