Dell Dimension 3000 latency issues

Just starting into LinuxCNC and have latency issues in the 500,000 range. Trying to wade through the details of SMI, etc but not following much of it. I ran the jitter test from the live cd and had what looked like reasonable numbers. Around 25,000 as I recall. I loaded Ubuntu 12.04 LTS thinking that was a good choice but was just reading that 8.04 might be better than 10.x for older hardware. But much of what I read about SMI and such seemed very dated. So I am not sure how much of it still applies. tried to run setsmi but got some errors that kept it from running. This newbie needs some help....

Here is some information on the PC. I haven't changed any bios settings yet.

Before worrying about SMI or other exotica, I would make sure that all power
management/clock speed options are disabled in the BIOS

Looked at settings in BIOS. Hyperthreading was already disabled. I disabled sound. There was a CPU speed option of "Normal" or "Compatibility". The description said Compatibility was "a lower compatibility speed setting which lets you accommodate speed-sensitive applications". I left it set to Normal.

I then ran the latency test from the 10,04 live CD. The numbers were very close to 25000 and 25000. (a 20x improvement!). I did the same thing with the 8.04 live CD. Almost the same: 25000 and 29000. I then repeated the test with the installed 12.04. Got around 500,000 as before.

It may be the the 12.04 install isn't optimized for LinuxCNC. This is an old machine with a CD drive (not DVD) so to get 12.04 installed I had to do an install of the OS and then install the real time kernel and then linuxCNC. So it is very likely something is not optimum. I could try to find an IDE DVD drive and install and then retry but I think I may just live with 10.04 and LinuxCNC2.5.0. I am open to ideas for newer version but I am not sure it is worth the trouble - I would welcome others thoughts on that.

I installed 12.04 as detailed in section 7.2 here:
linuxcnc.org/docs/html/getting-started/getting-linuxcnc.html

RAM on this PC is 1 Gig.

There is no reason to stay with Linuxcnc 2.5 on Ubuntu 10.04. Versions 2.6 and 2.7 both work perfectly fine on it. Updating is as simple as changing or adding the repository address and running an update (if you have an internet connection). If you don't then you have to download the debs and install them some other way.

Thanks Todd. I did find the instructions on updating and good to know it works fine. Looks like I need to go to 2.6 and then 2.7.

Any compelling reason I should be trying to get to 12.04 rather than 10.04? It appears I won't be able to do any updates (other than LinuxCNC) on 10.04 and I am not sure how installing packages I might need will work or not work since support has ended. But I don't think I will be needing much more than what is already included. This is only going to be used for machine control.