Hi
> Last year i had 400 users in my moodle course page. But this year there will be about 1500. Last year some of my students were complaining about unresponding pages or sometimes it resets itself. Before courses start, i need to know how many users can use this page at the same time.
You gave the answer yourself: barely 400.
> I am not sure if my server's configuration is enough for it. I know some softwares can test what IIS is capable of, Is there a possible way to test xampp as well?
There are many ways of benchmarking a machine. Some Moodle specific notes are given in http://docs.moodle.org/en/Performance_FAQ the first point "How do I benchmark a Moodle-site". That FAQ and the http://docs.moodle.org/en/Performance document are your starting points if you have performance problems (they were linked in the introduction to this forum).
> the server's configurations:
>
> - Intel Xeon e5335@2.00GHz (2 processors)
> - 12GB RAM
That's heavy iron!
> - Wİndows Server 2008 R2 standart
Well, that'll waste some fire power.
> - Apache Friends XAMPP (Basis Package) version 1.7.2
I hope you saw the comment "It is built to test web based programs on a personal computer. It is not meant for online access via the web on a production server." in http://docs.moodle.org/en/XAMPP
> Moodle 1.9.5.+
You should upgrade to 1.9 latest for better securiy. Performancewise 1.9 series is better than 2.x.