Low virtual memory

My macbook pro 2.26ghz version 10.5.8 with 2gb memory and running leopard is running very slow and when I run activity monitor it shows virtual memory size of 38.07gb. When I compare it to my sister's macbook, she has virtual memory of 104gb. What could be the issue?

How much hard drive space is unused on your MBP? If you have very little space remaining, Leopard can not build a large enough swap file (virtual memory).

I have unused 76.65gb..and used 72.0gb

Virtual memory is not the reason your MBP is running slow. You have plenty of free hard drive space. It could be a number of other things though. What I suggest is to download the free maintenance and clean up utility "OnyX". Read the instructions for using it and follow the directions for each step. Download LINK. Make sure you download the version for Leopard and not the one for Snow Leopard.