Hi,
your virtual memory is already enabled by default but if you want to make any changes you can find it by opening your control panel and clicking on System and Maintenance. Then click System and look down the left hand side for Advanced System settings. Look along the top of the revealed box for Advanced and click that. Under Performance (top of the page) you'll see settings, click that and then click the advanced tab along the top. You should now be at the virtual memory page. If you want to change anything just click Change.