Today my boss take ISA key file to us. I don't understand

"Kaspersky Anti-Virus BO for MS ISA Server International Edition. 250-499 Node 1 year Public Sector Licence"

Key description is 250 node 250 user

1. what mean 250 node?
2. what mean 250 user?
3. I can install this key to 250 server or not?
4. my customer has 2 ISA 2004 standard and 2 ISA 2004 enterprise
I can install all server by use only thiskey.


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