Run fewer programs! The easiest way to free up RAM and avoid the need for your computer to resort to using virtual memory is limit how much your computer is doing at once. If you have Live Messenger, Photoshop, Word, Excel, and Firefox open at the same time, your computer is trying to do too many things at once. It's going to run slower and possibly crash. When it nears its limit it tells you in a popup that you're running low on virtual memory, so simply close a few windows. Also keep in mind that having a few big files can be just as bad as opening several small ones.
Reconfigure your virtual memory settings. You can increase virtual memory your computer has with just a few clicks. Check how much RAM you have under "My Computer" and "General." Then to get into the virtual memory setup from here, click "Advanced." Click on "Settings" under "Performance." Then click the "Advanced" Tab. Next, under "Virtual Memory," click "change." Set the minimum and maximum for 1 1/2 times the amount of RAM you have. Once you've set this, restart your computer. If you make a mistake go back in the same way to reset the defaults.
Buy some RAM! Let the technicians know how much RAM you have when you speak to them (again, to find out how much you have, right click "My Computer," then "General") so they can help you decide how much more you need, based on the number and type of programs you run, including your operating system (for example, Vista should have 2GB while Windows XP usually needs 1). They will determine the type and speed of your current RAM, as well as what upgrades your computer is capable of (based on your motherboard). For example, some RAM modules that you buy need to be installed in pairs. Just be aware that installing hardware can void your warranty, so check with the manufacturer of your computer first. Good luck!