nadia,
I came across this little titbit today which initially looked promising: http://www.microsoft.com/en-gb/download/details.aspx?id=9258
This is the description which applies to it:
The Microsoft Windows Dynamic Cache Service will manage the working set size of the Windows System File Cache. For 64 bit systems this service helps to address the problem of excessive cached read I/O that could eventually consume all of physical memory. Sample source code and compiled files are included in the compressed file.
However, on checking the System Requirements, I note that it only applies to the following OSs:
Windows Server 2003, Windows Server 2008, Windows Server 2008 R2, Windows Vista
The odd thing about this though is that in was released on March 7, this year. I say odd, because Mainstream Support for Windows Vista ended in October 4, 2012.
As I understand it, Extended support kicks in when Mainstream support ends, but only applies to security patches. This release isn't one of those though.
You could maybe try running this Fixit which clears Windows Update cache to see if it makes any difference: http://support.microsoft.com/kb/971058/en-us
Other than that though, I'm afraid I'm at a loss as to what else to suggest.