How old of a PC still makes sense to use?

Hey, thanks for all the details.
Didn't help, though. (with regards to booting from DVD and not freezing immediately)

In WindowsXP on that machine, with that DVD-R drive, I can open the LinuxCNC DVD just fine, it isn't even struggling at all to read it (gauging from the *lack* of noise and delay the DVD has).
I see there is a windows executable "setup" on there, what is that? A viable alternate way to install it? I don't recall seeing that mentioned when I read some basic howto's.

---

LOL! This is weird and funny.
So I noticed that my DVDR was detected as master, HDD as slave, I reversed that. Didn't change the "freeze after boot from DVD". But when I booted from USB card-reader, the "detecting CDROM" screen appeared like last time, and it took ages like last time. BUT, instead of a failure notice, it said "Loading additoinal components", and you could see BOTH, the USB and the DVD to be accessing data now, for a while, so the setup actually did fetch some data from the drive, while moving a progressbar showing something was loaded.
Although I booted from USB.
This is rather peculiar!
I do not know now whether disabling the things you told to disable (why, btw?), or changing master/slave did this change, but it seems to be installing now.

---
I almost gave up for this evening because installing GRUB would remain on 3/4 progress for half an hour or so, and just as I wanted to turn off the thing, it goes to the "next page". That's now also taking long, mostly blinking the USB stick in funny patterns and hardly ever making the HDD LED visibly on. Is that normal, or only for my particular configuration of hardware of different degrees of outdatedness?

I let the latency test run for a while. Did not have an OpenGL application at hand as suggested. What I did was play one 1080p video from USB, and another one 720p from IDE HDD at the same time, using 2 instances of VLC, for a few minutes.

The times given are:
Servo thread (1ms): max interval(ns) = 1005292, Max jitter (ns) = 11332
Base thread (25µs): max interval(ns) = 36137, Max jitter (ns) = 11788

So 12 µs jitter for a thread supposed to run at 25 µs intervals (?), that's pretty rubbish, right?

--
Btw, the GRUB menu doesn't let me select anything (cursor keys not active, the USB keyb worked before when installing and the mainboard "PS2 / USB" jumper is on USB).

Actually that is relatively good latency for most pcs.

Newer doesn't mean better I had 5 times that latency on a core i7 and about the same on a coreduo.

The I7 was unusable even after I tweaked it following the forums posts.

Mmmmkay, 50% period jitter on the 25µs thread is "not bad"? Maybe I misunderstand those numbers. And then again, I guess the question is "bad for what", I'm not a motor expert.

Btw, I needed to enable USB legacy support for GRUB to work with the USB keyboard, although it works everywhere else without that. Weird, but good to know.

I've just been messing around with a Asus A8N-Dleuxe rev 1.02, 2GB DDR400, Radeon HD 7400 card and got sub 10000 latency, if it's of any interest........a whole lot better than the same with a Nvidia card. That was running GLX gears and watching video with VLC over a SMB connection.