We were getting regular BSOD crashes from TCPIP.SYS (more than one a day).
After googling for the crash message ( IRQL_NOT_LESS_OR_EQUAL ) I found threads that seemed to pin the blame on a problem with Zone Alarm and Vista.
Uninstalling Zone Alarm has certainly made the system more stable (no BSODs since then) but I am now relying on Windows Firewall.
This post is intended to document the problem here (for posterity) and also to ask if anyone has found a way to get ZA (my favourite FW) working satisfactorily with Vista. I’m not really that interested if you’ve NEVER had a problem, but if you have found a way of preventing the BSODs I would certainly be keen to know more.