Is the Dell Inspiron 531s(slim model) motherboard proprietary?

No surgery required.

OK, it will fit. Your Dell mobo is a microATX form factor. The new case will accommodate ATX or micro ATX boards.

You will need to remove your rear I/O header plate for the mobo and install it in the new case.

Just look at the pattern of the holes on your mobo and install the brass standoff's in the holes and put your mobo in and install the screws. The new case will come with screws and standoff's.

The only thing you have to notice is where the new front panel connections go on the mobo.

Make sure you know what pins are the power switch, reset switch, power led, and hard drive led on the mobo. The new case will have these wires labeled and they must go on the right pins.

I noticed you have a PCI-E slot on your mobo. You can get a video card and use it instead of the on board 6150 GPU. Then you could do some gaming when you are not busy.

If its the motherboard that has the problem then just remove the hard drive and place it in another Dell Inspiron 1150. save your info to disk and replace the existing hard drive back in the Dell Inspiron 1150. Or as john n say, instal it as a slave but will be a difficult task for you since it's a laptop you aer dealing with. That's the easiest way.

My experience with Dell mobos is there is always something non-standard, like the mounting hole patterns. Looking at your pix, you're going to need an ATX cover plate that fits the connector pattern of the motherboard. You could always drill holes in the motherboard mounting plate of the ATX chassis that match the Dell mobo holes. But the ATX cover plate will definitely be a problem. Will radiate lots of EMI if not covered so may mess up your audio electronics if they are in close proximity to your computer. How good are you with a piece of sheetmetal, a drill and a file?

you should be ok

your motherboard appears to be a "micro atx motherboard"

micro atx is pretty standard

and your case will fit that board

good luck :)