The simple answer is the MB is an ATX form factor. If the case is ATX compatible then the MB will be installable. If the case is a mATX (Micro ATX only), no the ATX board will not be compatible. A new case cost a little as $30.
Chiefvalue has a brand new Rosewill FB-02 atx case for only $20 shipped. The link is on fatwallet's website under "hot deals". Your old dell case may have a snap in board, which is proprietary. Check for screw holes and standoffs under the board, and see if the backplate where the ports are located can be removed. But I would order the case anyway for a spare; it will sell out fast.