Well it looks like you practically have a whole new computer in your closet, all that is missing is the case, ram, hard drive, and optical drive. If it were me, I would just buy those parts new and build it from scratch. And with that high-end of hardware, I would definitely go with a solid state hard drive. You could probably get all that stuff on the cheap for somewhere between $60 and $90 total. And then you have a brand new system.

Your old setup, btw, looks like it will support a max of Athlon XP 2600+, according to the MSI user manual. Honestly, I would probably just leave it as is (the cost of the upgrade from XP2000 to 2600 probably isn't worth the modest performance gain), throw in a GeForce6-series or Radeon x600/700/800 AGP video card and install Windows 98 or a 98/XP hyprid as the VIA chipsets on that particular board have readily available Windows 98 drivers. That particular hardware is kind of in the sweet spot for a 98/XP hybrid build; that is, if you have any interest in a Win98 system.

I have all those things, there's actually a big bag of ram on top of that stack if you can see. All of this, is what remains of both mine and my fathers old systems, it's been languishing in a closet for 5-6 years. Surely the Phenom II BE is an old granddaddy by today's standards.

The plan was alwYs to remove the Socket A board, but keep in the spirit what was there originally by placing another form of AMD chip back in. I have an Intel core 2 duo laptop which I use regularly, so I know I can manage to get everything done on a system of that spec. So my thoughts were to make an AMD equivalent using the Time tower case. Thus saving it from landfill and giving me a moderately spec'd old system to mess with.

I probably won't use the phenom II with it being such a power hungry beast, but both motherboards are AM2 so it does mean I can go for a modest processor that will perform daily tasks. It's a case of cracking a balance, usability and support for 10-20 year old software. I'm happy using dos box for those titles that are picky. But as I said much of my gaming will be Doom, Duke Nukem, Quake series, then onward in to early 2000 titles.

So scrub those boards, none of them have floppy support. In addition, the 125w Phenom II would likely have blown the PSU as others have said. Even if it would have worked at all.

Discovered I have a 2005 Q6600 I didn't know I had, I rescued it from a system my mate was skipping. I thought it was a bog standard intel core 2 duo. Didn't know it was one of Intel's first quad core CPU's.

Personally I would go with the Phenom ii and one of your compatible AMD boards. If you have even a compatible stock cooler and ram, and even a basic 80mm exhaust fan in your case with a low powerish GPU like a 550ti or something like that you can pretty much max out the XP era of games. All you would really need is a decent 400ish watt modern PSU. Im utilizing a HD 7770 and a Q6600 @ 3.0ghz with a Antec 380watt PSU in a Dell inspiron 560 with 7gb of ram as a temporary daily driver ATM. It is fairly usable as a modern web browser, even with the slow 250gb HDD it left the factory with. Been playing alot of newer titles with varying playability, but for older XP era games in my Steam library like CS: Source, Halflife 2, Halo CE etc. that I can run under Windows 10 it has been running excellent.

Check out some of PhilsComputerLabs videos on using am3/+ stuff and newer hardware as a XP machine.