How many threads are too many?

[rbt]

This may be a stupid question, but here goes:

When designing a threaded application, is there a pratical limit on  the 
number of threads that one should use or is there a way to set it up so 
that the OS handles the number of threads automatically? I am developing 
on 32-bit x86 Intel systems with python 2.4.1. The OS will be Linux and 
Windows.

I have an older app that used to work fine (254 threads) on early 2.3 
Pythons, but now, I get this error with 2.4.1 and 2.3.5:

Traceback (most recent call last):
   File "net_queue_and_threads.py", line 124, in ?
     thread.start()
   File "/usr/lib/python2.3/threading.py", line 416, in start
     _start_new_thread(self.__bootstrap, ())
thread.error: can't start new thread