When you open a program the program is loaded into your computer's RAM or Physical Memory.  When your computer does not have enough RAM or Physical Memory to run the program you want to open, Windows creates "Virtual Memory". Virtual Memory is extra memory that Windows carves out of any free hard drive space you have available. This gets you by so you can run the program but Virtual Memory is very slow compared to Physical Memory (RAM). So when you're out of RAM you can still run more programs but they have to loaded into Virtual Memory (specially allocated hard drive space). Because hard drives are inherently slower than RAM this means your programs will open slower. And the more Virtual Memory Windows is forced to use the slower your computer becomes. This is a very simplified description but it should give you and idea of why you don't want to be in a Virtual Memory situation very often.

What can you to do keep this from happening? The first thing is: Install more RAM. I notice you're using Windows XP. We strongly recommend at least 512 MB of RAM for Windows XP users. While you can get by (barely) on 128 or 256, you're apt to find yourself in a "Virtual Memory " situation often, especially if you don't control your start up programs and do a lot of multi-tasking. RAM is fairly cheap. Try to add enough RAM to bring your computer up to 512 or better, 768MB of RAM.

Control Your Start Up Programs: Make sure you check that you don't have too many programs starting with Windows. This can put you behind the eightball (sorry Eightball) from the moment you start your computer. Use MSCONFIG to disable as many startup programs as you can. Just remember not to disable any Windows start ups or your Anti-Virus, firewall or anti-spyware.

Reboot Your Computer more often. While Windows XP can run seemingly forever without rebooting, reboot it it every day need it or not, especially if you're having troubles with memory issues and cannot install more RAM at this time. So reboot your Windows XP machine after you're done using it for the day or the first thing in the morning. This will help to optimize your physical memory.

Windows 98/ME users need to reboot at least two, preferably three, times a day if they use their computers constantly. Windows 98/ME are very inefficient handling memory because the memory used by programs is not all returned to Windows when the program is closed, causing Windows 98/ME to eventually crash. The more programs you open the more memory is leaked.

Finally, keep your computer free of adware and spyware. Most of these types programs have many tentacles and install dozens of associated programs which not only start with Windows and burn up your available memory, but, are, for the most part, poorly programmed and rushed to market without much testing.  This leads to system freezes, program crashes and a multitude of other problems; not to mention the threat to your personal privacy. And to add insult to injury, Adware/Spyware uses your own precious system resources to show you advertisements on your own computer, controlled by an outside server, which we highly doubt you want to see.