When I boot up this system (a DELL OPTIPLEX GX110) it hangs at the DOS prompts before the system gets to the Windows screen. In the DOS prompts I am seeing the only error I can find which is "memory read/write failure.....Decreasing available memory" Then it finishes booting up and I log in and it hangs at the wonderfull blue screen of death untill I unplug it. I have swapped the power supply & the memory stick and the I reseated the CPU to no avail but I've never seen this error.

The entire error is as follows: "memory read/write failure at 0A38F12C, read 38D730D7 expecting 38D738D7 Decreasing available memory The amount of system memory has changed"

When I swap memory sticks it only says "The amount of system memory has changed" but it still hangs.

Has anyone ever seen this error to know what else I can troubleshoot?

Are you swapping the memory with the "exact" same type of memory?

You may have integrated graphics on that PC, where the graphics card-part has gone wrong. That is the only part of a PC that takes memory away the way you describe.
If there is an AGP-slot, try a card in there and see what happens.
Alternative is a PCI-graphics card.
In either case, see if you can disable the onboard graphics.

You might also try to go in your BIOS. There it might "shadow" ROM or Video-RAM. See if disabling that helps.

At first no but since you suggested it I swapped with another GX110 and I got the same result.

Also, if it were the memory card wouldn't I be getting a beep code. I didn't think it would let me log on (as far as I could log on anyways)?

Realblackstuff: I'm troublshooting everything else right now

Run an extensive memtest.