IIS 6 About 5% of request are very slow

Question

We have a IIS 6 web server on Win2003

The avg requests/sec = 200 The avg cpu utilization = 30% The memory 10% full HDD avg time = 5%

I have turned on the logging to see time-taken for each request and here what I see:

And here is the number of queries:

I have no idea why about 5% requests are working so slow. This is not only an application requests but static content requests too.