Memory Leaks

Hi all,
I am running an client-server application. For each client request the
memory usage observed in the task-manager is increasing by a fixed amount.
When I used the performance monitor with a counter for virtual-bytes used by
this process (sever process), it looks quite stable. The graph is almost
linear. But the memory usage shown by the task manager is increasing
constantly. Which one should be relied upon to decide about the memory leaks
? Is it the virtual-bytes counter for the process or memory usage shown by
the task-manager ? Does my application indeed has memory leaks ? How can
find whether it has memory leaks or not ? Any help is appreciated.

Thanks,
Nagesh Bhattu