Windows XP does a great job at managing memory - add on "memory managers" actually defeat proper handling of memory and are not recommended.
It is not rare for memory to go bad, or even new memory to be bad.
Run a couple of the following Ram tests:
Myth - "Increasing the amount of available RAM improves performance."
Reality - "RAM Optimizers have no effect, and at worst, they seriously degrade performance. Although gaining more available memory might seem beneficial, it isn't. As RAM Optimizers force the available-memory counter up, they force other processes' data and code out of memory. Say that you're running Word, for example. As the optimizer forces the available-memory counter up, the text of open documents and the program code that was part of Word's working set before the optimization (and was therefore present in physical memory) must be reread from disk as you continue to edit your document. The act of allocating, then freeing a large amount of virtual memory might, as a conceivable side effect, lead to blocks of contiguous available memory. However, because virtual memory masks the layout of physical memory from processes, processes can't directly benefit from having virtual memory backed by contiguous physical memory. As processes execute and undergo working-set trimming and growth, their virtual-memory-to-physical-memory mappings will become fragmented despite the availability of contiguous memory." - Source
Registry Cleaner Registry Cleaners
Myth - "Registry Cleaners improve performance."
Reality - "A few hundred kilobytes of unused keys and values causes no noticeable performance impact on system operation. Even if the registry
there would be little impact on the performance of anything other than exhaustive searches." - Sourcehttp://mywebpages.comcast.net/SupportCD/XPMyths.html