virtual memory is determined by multiplying 1 1/2 times the actual memory that is installed. In your case you have 512MB of memory (which is really in-adequate) so the virtual memory should be set to 768 or a bit more. To change the virtual memory or what is also called the "page file" :
1. Click Start, right-click My Computer, and then click Properties.
2. In the System Properties dialog box, click the Advanced tab.
3. In the Performance pane, click Settings.
4. In the Performance Options dialog box, click the Advanced tab.
5. In the Virtual memory pane, click Change.
6. Change the Initial size value and the Maximum size value to a higher value, click Set, and then click OK.
7. Click OK to close the Performance Options dialog box, and then click OK to close the System Properties dialog box.
You should check what your "available memory" is ! if it is less than half of what you have installed then you should look into adding more memory.
Start > all programs > accessories > system tools > system information and scroll down to the actual installed memory and the available memory listing is.
google for this utility as it sometimes helps in matters such as this....
UPHclean from microsoft.