Steve - this is my personal

Steve - this is my personal opinion, based on a bit of experience.

Old computers need to be recycled.  They may function, but they are just waiting to die.  Probably at the worst moment.  Yes, you can replace the hard drive, etc. but I don't think you are looking for a new hobby.

The best thing I ever did was replace the computers I had been using with a Raspberry Pi for JMRI.  It's cheap, much better than anything running XP, and fully supported.

The best thing about it is running all of the software from the SD card. Once you have everything running to your satisfaction make at least a second backup copy. Use the built-in card copy utility.  You will need a plug-in card reader to make the copy. (so you can plug in both SD cards at the same time.)

When It comes time to upgrade or make modifications. Make them on the copy. If they don't work, just put in the other working copy and go right back to running trains.  Yes, you can do backups with your old XP system but it takes time and is a pain.

Copying the SD card on a RPi takes a couple of minutes, and now, it's even easier with the built-in utility.

If you don't want to recycle that old computer, I'm sure there is a boat that needs an anchor.  That's about all it is good for.

Just my opinion, gs

+1 for Raspberry Pi

what about windows applications?

i'm all for a raspberry pi and the stability of linux.   but what if he want to run a windows applications?

Windows 10 on Raspberry Pi

A fresh Win7 on a reconditioned PC

Steve, if I read correctly your question, I would suggest to stay with Windows. Linux can be an alternative, but it may (-will-) require anytime a geek level. And any piece of software or driver that does not have a Linux version will let you stranded in the middle of nowhere.

There is a "Windows for Linux" layer named Wine, that runs many Windows softwares under Linux. To be precise, the Windows API (Application Programming Interface) have been re-written to interface instead with Linux. Works amazingly great with a certain number of softwares, but refuse any service with others. Again, not for non-geek level.

Arduino and Rapsberry are promising and neat thingamabobs. They have great merits, but work with a different logic. In my modest opinion, they are a true hobby in the hobby, too.

As for old PCs that are future dead PCs, that applies to brand new PCs as well. And a club I visit from time to time still has one IBM PS/1 that runs the HO layout. And an IBM PS/2 for the N layout. Both work like Swiss clocks under DOS 6.1 and tube displays, and there is no plan that I know of, to replace them.

If it were just for myself, I would stick with Windows because it is the environment you know. But I may go to the nearest PC store, that most probably will have some reconditioned one with a fresh Win7 for $100 or about. It is an OS still sufficiently recent not to be concerned with software versions (i.e, many peripherals do not have drivers for Win10). If you consider a laptop, check it has as many USB ports as possible.

And to anticipate that sad day the reconditioned PC would go to Paradise, may I give you the advice of what I do. For each and every piece of software I install on my PC, I write down each and every option or parameter I go through during the installation. I do it for a fresh cold install of Windows, up to the smallest stadalone utility. Frankly, it's cumbersome. But in case of a disaster, I can re-install everything on a new, working hardware, in a couple of hours. Instead of days if not weeks, of guessgineering to remember everything.

But it's only my humble opinion.

might consider a brick

$240

My old computer that I used

My old computer that I used for JMRI and also my laser had a hard drive crash.

I replaced it with one of these, working out really well. It is a small form factor and dead silent.

https://www.ebay.com/itm/HP-ProDesk-400-G2-Mini-Intel-i5-8GB-RAM-500GB-HDD-Win-10-USB-VGA-B-Grade-Desktop/283916588872?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

An even cheaper Windows mini PC

$130 ... free Prime shipping 
https://amzn.to/3gNZktR

RPi

First as the OP stated:

SInce there is no need for a windows PC, go the RPi route, with Steve Todd's image you can be up and running with JMRI and connect to your DCC system in a very short time.

If you want to go the PC route, check out newegg.com for refurbished PCs, they don't come with monitors, but do include a keyboard and mouse if I recall correctly.

Hi Steve...

As someone who has just upgraded my PC for my layout, I can vouch for the refurbished route so long as its within a few years old and the HDD has been replaced with a SSD (Solid State Drive) Version.

I upgraded to a Dell - Optiplex 9010, after my old Dell couldn't support an upgrade to the motherboard for a new digital display card upgrade.  The advantage for me was the multiple display ports and DVI on the Optiplex, it allows me to run triple monitors at my dispatchers deck for layout operations.

Also an added bonus is the multiple USB inputs too, you'd be surprised how many you need for a layout.  At $259 AUD it was an absolute bargain and perfect for running a medium sized layout.

Jas...