i have win 2003 server with iis6 server performance shwo that w3wp.exe use 765.502 k from memory in the normal use 97 or 90k
i was read about thes problem and i fined Relationship between thes problem and web sites use asp.net i have a lot of web sites use asp.net i need tool help me to fined thes web site
If you host a lots of websites, you may at first create few groups of new application pool and assigned the websites to each pool accordingly and monitor the memory usage from pool and from there you will be able to split out further for the application pool and finally get the websites.
Other than that, you may also download FileMon to check which websites are having heavy http queries and from there look further.
Like tweakservers said, make multiple application pools and assign websites to these pools. Per application pool you can set up memory limitations. Further, most probably the huge amount of memory consumption is caused by bad programming of (at least) one of the websites. Think of opened but not closed database connections and so on.