As well as reading through this article,
http://windows.microsoft.com/en-gb/windows/preventing-low-memory-problems#1TC=windows-7 perform a clean boot.
That is when you go Start - type msconfig and press enter then under the Startup tab hit the Disable all button - Apply - OK.
After the reboot go back into msconfig and ensure if the AV program is one of those start up items that it is running, or you can re-check its box after hitting the Disable all button but before you hit Apply etc.
Paid for AV programs will auto reinstate themselves as soon as you hit the Apply button but some of the freebies don't.
Unnecessary programs in Start up will be unnecessarily be taking up memory - I only have one in mine and that is for my printer.
A defragged HDD will also aid Virtual Memory so that is something else worth checking and then see if you still get the insufficient error message.
Before you defrag/analyse the HDD, go Start - type %temp% and press enter, if that is highly populated then click on Organize - Select all - Organize - Delete - confirm - check the box then click on Skip and close the window.
The Recycle Bin will need emptying then.
It's surprising how many people don't maintain their computers.
Win 7 has it's own tools as well in Control Panel - System and Security/Find and fix problems to use the maintenance and performance tools.
If the HDDs are getting low on space then you can free up some - poss. up to 3GB by going Start - type disk cleanup - right click on Disk Cleanup and Run as administrator.
This will scan for obsolete Windows Updates and add those to the other default items which is normally sufficient.
If the HDDs are really short on free space and the owners don't use Hibernate, you can turn that off in an elevated cmd prompt with the cmd powercfg -h off and that will free up about 6GB.
A defrag after that may also be warranted.
