How to determine no of work Processes in IIS 6.0

Hello,

I am complete newbie in IIS world.
I am working on application which uses IIS 6.0 with 2003 server.We are using our won application pool for which 2 work processes are running in task manager.

I have been asked by my client that how we can increase no. of work processes.

I need to know like on wht basis we can determine no. of work processes. On which factor no. of work processes is dependent n is it feasible to increase it??