For the bad news first...as far as swapping your motherboard into a new case...not really..the motherboard is in BTX form...meaning the I/O connectors...mouse...keyboard...video...lan...sound...are all reversed.
When looking at the back of your case...all those connectors are on the RIGHT side of the case...in standard ATX form...this is REVERSED...all the connectors are on the LEFT side of the case..so the motherboard orientation is reversed in your mini-tower case...you can't just turn it around...the connectors would then be facing the front of the computer case.
Look Here
http://support.dell.com/support/edocs/systems/op745/en/UG_en/mtindex.htm
That's all the specs and images for your rig.
Sorry I couldn't be more helpful!
The good news here "I guess" is that the Mini-Tower CAN accept a standard ATX psu...not a lot of help I know but DELL is all about proprietary equipment so that the only folks working on them are DELL certified technicians...read as MONOPOLY!
Sorry about that but the facts are just that...the facts.