This FREE tool clears out your current data sets in RAM. Basically it reclaims your used RAM

Clearmem (clearmem.exe) -Forces pages out of physical memory and reduces the size of running processesf working sets to a minimum. When you run this tool, the system pauses because of excessive high-priority activity associated with trimming the working sets. To run this tool, your paging file must be at least as large as physical memory.

Put clearmem.exe in your c :/windows/system32 directory, then go to Start -> run and type clearmem

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Enjoy,
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Source: XP-erience.org