Lg CRT monitor model 500g 17inch -out of frequency (by 2 users)

First, you did a great job of explaining and starting to identify the problem. You also eliminated a few things that we would have tried along the way.
PROBLEM DEFINITION: The real issue (as you may already know) appears that the operating system, specifically the software drivers for the video board and monitor, must be correct in order for the monitor to work. In other words: there are three computers that must be able to communicate with each other - the main computer, the video board computer (microprocessor) and the monitor's computer (also a microprocessor). Think of the drivers as the programs for each of the microprocessors. The message you are getting says that one of the three programs is sending data to one of the other programs and that the receiving program is complaining that it is "talking too fast to understand".

So, which one? Since you are not having any problems with Win98 or 2K then it is not a problem with the monitor (or so it seems). Since each Windows operating system must load its own driver, and many times these drivers are not the same (actually the "kernel" is if you think of them as programs for the microprocessors) because they must talk to the operating program too. I'm puzzled about the "...safe mode...didn't work..." comment since safe mode doesn't load the drivers on purpose. Maybe it worked at first and you didn't change anything so it didn't work when you logged back on without safe mode?

POSSIBLE SOLUTIONS:
1. Start up in Win2000 and look at "properties" for the video board and monitor. Use "advanced" if necessary and write down all of the driver names, the make of the vidoe board and especially the "frequency" of the monitor that it "thinks" it is. If it is "auto" then see if there are any other choices (50,60,65,70,72 and 75 are all popular sweep frequencies). Note that the video card AND the monitor must be able to communicate at the SAME frequency. One of them (or both) can be on "auto" but one can't be on 60 and the other on 72! This will produce the error message you describe.

Now, try to start up your WinXP (safe mode if possible) and fix (match) the properties/frequencies. You will have to bring up the control panel to do this since the "properties" selection is locked out in safe mode.

2. If this doesn't work then it might just be a program that is loading during startup. Check the "run=" statements in the Win.ini and system.ini files for WinXP. Remove or comment these out. An older game or application that didn't work on WinXP may try to grab the video before the system would start. Eliminate, or comment out if you don't want to eliminate any that you might want to keep, any program that you suspect or just don't have a clue what it does. Suspect programs that load on startup are virus checkers that were not written for XP.

3. Save, preferably on a removable device (USB thumb drive) your current video card and monitor drivers for WinXP as a backup. Log in using Win2K, download current drivers for your video card and monitor, also onto the thumb drive. Then, delete the drivers from the device manager. When you restart it should say "found new device" for both the video card and the monitor. It should then ask for the drivers. Point it to the thumb drive and load the new drivers.

Please rate this solution and let me know how it turns out...