I happened to see this thread while I was searching the performance forum and thought I would share our experience with you...
I would be willing to bet that the problems you see being described here are classic examples of a very well known "memory leak" problem that occurs when using Windows 200x as a server with PHP and Apache Web server.
This selection of software has a very poor record on the whole for supporting larger, more active sites.
Do a Google search on Window 2000 or 2003, PHP, Apache 2.x and the phrase "memory leak" and you will find hundreds of people complaining all the way back (3-4 years or more) about this exact type of problem. (e.g. Apache server under windows with PHP will have its child processes (the workers Apache web server starts begin to eat memory and never release it until the server becomes completely unresponsive)
Typically when you see the HTTPD.exe or Apache.exe child web process consume about 400 to 1000mb of RAM the Moodle server will freeze - you can watch this ugly memory process grow hourly in the Windows Task Mgr if you want....
My team tried about 15 combinations of Win 2003 server, PHP 5.x and Apache 2.x and they ALL did the same thing - ie. leak memory hourly under a Moodle load. We talked with sites all over the US and Europe and most people were doing ugly "hacks" like limiting the MaxRequestPerchild and doing a nightly or daily re-start of apache to keep things going. We looked hard and to my knowledge no one has ever solved this issue. (see the ApacheLounge website which focuses on Windows and Apache support )
Some people gave up on Apache and used IIS with some success. Others like us went back to some type of linux OS which works well with Apache/PHP and releases memory properly and has no "memory leak"
Hardware and performance
Memory runs out on new server
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