JMeter server on solaris

[Yuval]

Hi,
 I'm trying to run a load test (web) with the jmeter server running on a 
Solaris machine.
The problem is that it seems like I can run only ~500 users, while the CPU 
is only around 35% and the memory is on 25%.
 Anyone knows if there's a limitation of the max number of threads per 
process on Solaris, or any other cause for this issue?
 Thanks,
 Y.