if you have a a box from http://www.onesecure.com you can put you IDS inline with your network.... The smart thing about the onesecure box is that it can also do prevention.

they say

'The OneSecure Intrusion Detection and Prevention (IDP™) system effectively secures your network'

This is an intel server style box with multiple nic's.. The core software is built by a break away group of FW1 engineers and can import your objects from FW1. due to the fact it can run inline its a true 2gen IDS system...

and no i don't work for them ;-)