What Duke says is right. Generally all cases you find on Xoxide are going to fit components(the motherboard is what specifically people worry about putting their hardware in a new case).
As I sit here I reply to a pretty much dead thread.. I have a Dell PowerEdge 400SC and I need a new case.. I was told (by reading an unofficial faq) That it doesn't fit under the ATX specification. It is held to the motherboard tray with plastic standoffs and 4 screws, none of which are in the locations specified by the ATX standard.
So what do I look for? I don't like dealing with Dell so I have no clue what kinda case I need.