As my emachines MBs have died, I have just swapped my HD into replacements,
Now I see a lot of Dell GX270's on ebay. (XP PRo)

My emachines HD (T2642 - IDE 40GB) is Home XP.
Can I put in my HD and make it work.

Alternatively: is there any non-emachines system I can put it in and make it work

Yes it is possible but very tricky and depends on the type of Windows product key you used. If the Windows XP on you eMachines HD came with your system, it's OEM and you're SOL! You can't use an OEM branded Windows product key on a different manufacturer. If you installed Windows XP from a retail copy for your eManchines, then you can re-use the HD but you need to perform a Windows Repair to get it to "fit" the new system. Even at that, there may be some device drivers missing and you have to look them up and install them manually.

-- Andy

I would say it is going to be tricky, unless you match the hardware. I think you will be better off buying a new computer & a new HD and just use your current HD (with all your data on it) as a backup.

BTW
Welcome to TechSpot

Again, if your e-Machines came with Windows XP, that's an OEM product key. This means you can't use that HD on any other computer except the same e-Machines model you had. Now if your pruchased the Windows XP then that's a retail product key and you can, by using Windows repair feature, be able to install the HD on another PC.

-- Andy