COPMOM - it's virtual memory (stored on the hard disk as a file named pagefile.sys) and to get rid of those pop-ups do this:
1 In the START MENU, right-click on MY COMPUTER
2 Select PROPERTIES from the menu
3 Select the ADVANCED tab
4 Click on the SETTINGS button in the PERFORMANCE section
5 Select the ADVANCED tab that you now see
6 Click on the CHANGE button in the VIRTUAL MEMORY section
7 Change the setting from SYSTEM MANAGED SIZE to CUSTOM SIZE and set the INITIAL SIZE and MAXIMUM SIZE settings to the same value - some people suggest it should be 1.5 X you total RAM (n.b. the input value is MBs so to set the virutal memory to 3GB you enter a value of 3000).
One downside of a large value is that your computer will take a bit longer at startup because Windows has to read and process the contents of the Virtual Memory file.
(If you want I can give you info about a utility that tells you exactly how much virtual memory your system expects and you can thus find a setting that is sufficient for Windows whilst reducing that start-up time to a minimum)