2GB isn't a lot of memory for Windows 7 64-bit. I'd recommend 4GB as a minimum.
We had a few PCs at work with 3GB and they would start thrashing the hard drive (virtual memory) as soon as we opened up a program or two due to lack of physical memory.
What is your video card situation? Are you using onboard video? If so, how much physical memory is allocated to it in the BIOS? It's possible that it's using 1/2 or more of your physical memory.
Related to the above question... What resolution are you running your monitor at? Higher resolutions require a larger frame buffer, which I believe comes out of physical memory when using onboard video.
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