No, you’re not screwed over. I’m saying your Dell is old enough that it uses the standard ATX configuration, just looking at the pictures. Your components “should” fit into a regular ATX case.
Most motherboards differ a little bit on the configuration of the wiring headers for the power switch, reset switch, led for hdd ide activity, power led and the speaker. This is normal. You’ll just have to see if the leads on the wiring included with a new case match up well to what is on the Dell motherboard. Sometimes you have to improvise, and moving an oem motherboard into a generic case, you are more likely to find this situation.
Luckily for you, all the modern Dell motherboards use standard power supplies. Back in the PIII days, they did not.
My only worry on this particular move is the configuration of the holes in the motherboard, and how it fits onto the standoffs of the case. It should be standard ATX or MicroATX…a regular ATX case can accommodate either of those. As I said before, I doubt this motherboard is non-standard. It would increase costs for Dell.