To answer one part of this question: you need to pass a full path to "java.exe" to the command you use in the batch file. Alternatively, modify PATH environment variable to add the path to this file. If Java is not installed at all, install it.
As to the number of users set for Apache JMeter, you did not explain what was the problem to add more than 250 users. Did you try to search JMeter documentation?
http://jmeter.apache.org/usermanual/index.html[
^],
http://wiki.apache.org/jmeter/[
^],
http://wiki.apache.org/jmeter/JMeterFAQ[
^],
http://jmeter.apache.org/api/index.html[
^].
[EDIT]
Answering the follow-up question about Java installation.
You should first check up the prerequisites of JMeter and check up if it includes Java installation or relies upon the user's installation of it. Usually, the applications rely on the Java Machine by Microsoft or Oracle (formerly Sun Microsystems recently merged into Oracle Corporation).
It looks like you need to learn what Java is. Please see:
http://en.wikipedia.org/wiki/Java_%28programming_language%29[
^],
http://www.java.com/en/[
^].
Download the Oracle installation:
http://www.java.com/en/download/inc/windows_new_xpi.jsp[
^].
—SA
Submit an article or tip