Want to swap to an HTPC case

Being a Dell, I wouldn't count on it being a standard size. You might want to call or chat Dell and find out.

Dells and most OEM PCs from HP, Compaq, etc., tend to use proprietary hardware that may or may not fit in standard PC cases without special brackets. Same goes for using off-the-shelf hardware in a Dell PC. They only want you to get your hardware from Dell and nowhere else so they make it extremely difficult for the consumer to do so. It's the very reason why I'll never buy another PC from any of the big name maufacturers.

I had a Dell Dimension 2400 and used the case for my HTPC. I took some rough measurements of its mobo's mountings & their spacings appeared to match the uATX mobo that I bought. I was also lucky enough to find a website where someone did a mobo swap with a Dell 2300 & it worked.

In my scenario the Dell mobo & the one I bought where interchangeable. You might want to measure your Dell mobo mountings & compare them to a standard mobo to see if they are the same. If so then hopefully your mobo will fit a standard case.

I also used a standard size power supply & it matched the Dell in size & mountings.

The motherboard is one of the few items in a Dell PC that probably adheres to standard mounting configurations. If it's either an ATX or micro-ATX board the mounting holes should line up with those in a standard case. The main items that might cause problems when trying to transplant Dell components into a standard case is the optical drive and floppy drive. Sometimes the front of the case is used in place of an actual bezel on the front of the drive and sometimes they require non-standard mounting brackets to secure them to the case. They also use funky shrouds over the CPU cooler to direct airflow that might not work in another case. You might have to get a different CPU cooler if this is the case, but you'd have to check to be sure. One thing you could try first is to see if the various components will fit in any standard case before buying a HTPC case. If they'll fit in a regular PC case they should fit in the HTPC case as well, assuming you don't have components that are overly large, such as a long graphics card.

You're right about the "funky shrouds over the CPU cooler". My CPU fan was not mounted on the heat sink. It was mounted on the back of the Dell case with a plastic shroud or duct going from the fan to the heat sink. I would have needed to buy a CPU fan if I moved the Dell mobo to another case but am not sure how or if possible to attach to the Dell heat sink.

It's been my experience with trying to salvage parts from several old/slow dells that EVERYTHING is proprietory! Recently I tried to salvage a case and power supply for a new cheap workstation build from a dell 2400 and the power supply cables would not reach the new MB so I buy a new power supply and find out the cables from the on/off switch, usb, hdd light etc wont reach! This was with a m/atx board.

I put a mATX mobo in the Dell 2400 case & I know some/all the cables from the on/off switch, usb, hdd light, etc just reached. IIRC I had to un-twist one of them a few turns in order to get just a bit more length. The mobo I used has only 3 PCIe slots instead of the typical 4, so it was slightly smaller which probably helped.