Dell used a proprietary pinout on some of its PSUs a while back (same connector, just different arrangement of wires in it - pretty stupid of them, IMO, and quite dangerous). So you have to be sure it's the standard pinout before using it on a standard mobo. If you are a techie, you can get a pin remover and rearrange the pins in the shell or you can get an adapter cable for the less adventurous.
Looks like you have an SFX size PSU probably very low wattage - saved Dell a few sheckels... Looks like a standard I/O shield that will come with your new mobo should fit. Looks like a standard ATX mobo will fit - the Dell has a short mobo, standard is 9.8" deep but some standard mobos are shorter than that due to the more highly integrated chipsets that are available. But you'll need to find some of the clip type standoffs to fit the extra mounting holes. The cooling is non standard too, so you'll have to jerry-rig something to work with a standard mobo.
If it was me, I wouldn't want the aggravation of trying to rebuild in a cramped little case like that. Plus the difficulty of finding a reasonably powered PSU in that size. I'd go for moving the stuff into a standard ATX case that will hold a standard ATX/PS2 sized PSU.
They may still have some SLK3000-B cases at the Antec B Stock store for $22. + shipping. Very nice case. Nope, they don't but they do have the Super LANBoy which is also very nice. Shipping costs from Antec can be outrageous though. Careful shopping will find you a good case at low bucks. The Rosewill R5600 series has been on sale at Newegg and is a great sturdy case that would last you thru several changes of internal components.
.bh.