There are really no perfect solutions for fixing memory errors and incompatibilities. Most often trial and error protocols work. Most softwares for diagnosing memory problems can't really give an "ultimate solution" for solving every error that occurs since there are so many configurations/variables/parameters/platforms, etc... involved. However, they may help you find out more about the particular problem in the immediate term. Long-term diagnosing is unpredictable since components change over time. Simply put, compatibility will change since a user may change his or her platform by upgrading or downgrading the appropriate softwares and hardwares.
Here are some links of softwares that will help you out at least for now:
Memtest is highly regarded and very advance. Some softwares mentioned are freeware, while others are payware. Others in the forum may suggest alternatives as well. Place a thread asking other members what memory diagnosing softwares they find most useful. Opinions will vary of course.
Remember before you try any of these softwares, it is best to first do trial and error analysis. Experiment with various memory modules in various dimm slots. Make sure to clear your mainboard's cmos first to reset your bios before installing any hardware. Make sure to upgrade to the latest bios if necessary and make note of the compability improvements listed for that latest or most recent bios revision/firmware/upgrade. Go into your bios and make the necessary changes to it to accomodate the newer rams to their respected specs. For example, if the memory is capable of dual channel, then you may have to manually tweak the memory configuration part of the bios to fully accept the newer rams' specifications. This will depend on your ram and mainboard's individual specifications. Some of the newer and more recent rams and mainboards automatically configure and detect the appropriate specifications without any real hassle. Consult both your ram and mainboard specs to make the correct changes in the bios. Go to your mainboard and ram websites if available and download and read the appropriate faqs/revisions/firmwares/bios upgrades/any other pertinent softwares, etc...
Generally you press "delete" once you see your computer go through its cpu and memory diagnosing stage to enter most mainboards' bios. It may be a combination of "ctrl delete" or F1 or Tab, etc... Often times with newer boards, you'll get direct instructions on how to get into the bios at the bottom of the screen or stage when the cpu and memory are being detected as your computer boots up.
Once the hardware troubleshooting part is done and you're back into windows. Run dxdiag to see if most if not all of your system specs are correctly identified. Use the "run" box in your taskbar and type "dxdiag" and then click ok. In addition go into your control panel and system performance tab and then system properties to see if the cpu and ram are correctly identified. You may also have to install any newer mainboard chipset drivers if available and the improvements listed in those particular drivers have the potential to solve any real compatibility issues with either softwares or hardwares of various types.
Other softwares that may be of some importance are wintools professional, wintask professional, sisoft sandra professional 2005, pcbugdoctor, tweak xp, registry mechanic, pc doctor, spyware doctor, windows washer, spy sweeper, and many others not listed for the sake of time. I'm sure other members can recommend many more useful alternatives.