Your system is low on virtual memory

I am running Windows server 2003 on a network in my workstation. I have altered some personal settings like theme and screen saver and while applying these changes, I got en error message like:
Windows – Virtual Memory Minimum Too Low
Your system is low on virtual memory. Windows is increasing the size of your virtual memory paging file. During this process, memory requests for some application may be denied. For more information, see Help.
Need assistance from people who can help me to solve this problem.
