With XP, I had a similar problem related to a Maxmem setting in the boot.ini. I had just added another stick of mem, but sysinfo didn't reflect it and there was major swapping. I got rid of the maxmem option, which was set by an old Matrox video driver, and all was right in the world.
MS on maxmem: http://msdn.microsoft.com/en-us/library/ms791488.aspx
There might be something similar in Vista.
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With XP, I had a similar problem related to a Maxmem setting in the boot.ini. I had just added another stick of mem, but sysinfo didn't reflect it and there was major swapping. I got rid of the maxmem option, which was set by an old Matrox video driver, and all was right in the world. MS on maxmem: http://msdn.microsoft.com/en-us/library/ms791488.aspx There might be something similar in Vista.