Ramana,
As the previous posters have said, consider increasing your RAM. When an application's computing does not fit in RAM it then uses hard disk space as a slower alternative for storage and it is called virtual RAM. How much RAM do you have ? In XP you click on Control panel, System, Advanced tab, Performance settings, Advanced tab, and finally virtual memory change.
I run Intellicad and using a custom setting of 760 MB (min) to 1540 (max) produces no complaints while running big files in Intellicad. Your system is different so play with these numbers till you get a satisfactory result.