Ubuntu's LTS is 12.04. I plan on running it until the next LTS version comes out in April 2014 or until April 2017 whichever suits my mood.

I hate the Unity desktop, so I went with Gnome Classic. Not sure what is going to happen with 14.04 LTS.

Anyway, you may look upon this as an opportunity to play around with Linux and learn more about it.

Money spent on a new OS whether Window 8.1 or Windows 7 is better spent on a new PC. My 2cents.

I have an XPS G4, which is basically the bigger, football-playin' twin brother of the 8400, and it runs Windows 7x86 superbly.  The game port on the sound card is the only thing that does not work in Windows 7 (big deal).  I haven't played with Ubuntu on this system, but I don't see any reason why the 32-bit version wouldn't work (not sure how your graphics would handle Unity though ... graphics options were one of the few difference between the XPS G4 and the 8400).

For now I will consider this issue partially resolved... I installed DouDou linux on it for the kids (and the youngest liked it, the older ones thought it too childish), so I reformatted it with SuSE 12.1. It is running fairly smooth with that - at least as smooth as an older computer can anyway.

Any reason why you chose SuSE 12.1 when OpenSUSE is at 13.1?

I was not 100% certain it would run, and so I downloaded 12.1 to test if it would install. It seems to run well, so I will see about upgrading later. The key is that it works,

Usually with the older hardware, Linux works pretty well. Glad you have new life for your PC.

My main concern now is getting kids games to run on it... That is a series of questions for another forums I think though.

I may try a few other distros when I have the time too, just to explore and have fun.

Any input as far as OSes known to work with this model would be awesome.

Windows 7 32-bit would work, and the 64-bit version would work if you replaced the CPU. (Used CPUs can be had cheaply on eBay.)

What 64 bit CPU is compatible with the Dimension 8400?