I'm not sure what you mean by "ping thresholds", but you can change the discovery timeout and retries by setting up separate discovery ranges for each group of servers.  If you are talking about the Status Polling settings, those are global for ITA so you would have to set up multiple instances of ITA to do that.  If you are trying to monitor multiple sites or subnets I recommend putting an instance of ITA in each site or subnet because SNMP does not travel well across WANs or the Internet.
I'd like to setup IT assistant to have different server groups with different ping thresholds. What is the easiest way to do this?
IT Assistant 8.0