This will depend on the application tested, the scenario and its parameters, particularly the think time between pages: a Load Generator can generate approximately twice as heavy a load with a think time of two seconds than with a think time of one second.
Likewise, generating a load using HTTPS (SSL) and using modules such as Flex, GWT, Oracle Forms, Java Serialization, RTMP and Siebel use up more machine resources than with HTTP.
As an example, a Pentium IV 2.4GHz can generate up to 1500 Hits/sec. A Load Generator typically can generate between 500 and 1500 users on a standard application.
It should be noted that the NeoLoad Controller can use as many Load Generators as is required to generate the number of users specified in the license, at no additional cost.