Java EE (Java Enterprise Edition) General Discussion

I need to use Tomcat as a plug-in on IIS for a project.

I make the whole installation (Tomcat, IIS and the ISAPI redirector) without any problem (I am used to do this sort of installations).
But doing some loading tests, I encountered very slow performances : 50 simultaneous users on a very basic web application and the server is full...
Of course, if I do the same test on Tomcat without IIS (with the HTTP connector enabled), there isn't any problem...

The installation seems to be OK, the physical server is a pretty good machine...
Versions used are :
- Windows 2000 sp2
- IIS 5
- Tomcat 4.0.3
- isapi_redirector.dll released with Tomcat 4.0.3
- ajp connector 1.3 (aka ajp13)

Does someone have the same problem ? Or does NOT have this problem in the same context ? Is there an alternative to using this ISAPI filter (but still using IIS and Tomcat) ?
I noticed that lots of people still use Tomcat 3.3. Is it too early to use 4.0.x series ?

Every piece of info would be useful...
Regards.