I've used my old Dell Inspiron 537 quite a lot for testing various hardware I come across, to the point that I've totally disassembled the case to make installing stuff easy. That said, there is one thing that sucks about it: having only 2 SATA ports, and having no floppy header. So, to remedy that, I swapped out the motherboard with a similar, but slightly older Inspiron 530 motherboard that has both 4 SATA ports & a floppy connector.
Removing the original motherboard was fairly easy, but there was one problem: the I/O shield. The I/O layouts on the Inspiron 530 board are just a little bit different, so I had to remove the old I/O plate to install the new motherboard. Unfortunately, it was too stubborn to come out normally, so I wound up having to smash it out of the case with a hammer.
The 2 boards are 2 different sizes, but the case still had the screw holes to install the new board. The proprietary front panel connectors still worked with the new motherboard, which was lucky.
The first time I turned it on, I forgot to install any RAM, and it jumpscared me when it went nuts & started beeping insanely loudly. Anyways, I just stole the 2GB stick from the original Inspiron 537 board & used that, since I don't have any working DDR2 RAM at the moment.
The motherboard has a rather lackluster 2.3GHz Core 2 Duo installed, but since it's just a testing rig, it barely matters. But, if you need to use the Internet from it, it's gonna be pretty slow.
I haven't gotten any new equipment over the past few months, but now that the basement is fixed up again, hopefully I'll get back to finding more computers.