Have you created a trusted network for your router/network card? If not perhaps you should - this will cut down the amount of logging considerably.
The high CPU usage may be partly due to the firewall writing to the log file. You could try disabling logging to see if there is any improvement.
In network monitor right click any block and log rules and select edit. Uncheck the box 'create an alert if this rule is fired'.
You can always turn this back on later if you wish.
Another option which can help and will still allow you to view some log events is to make the log file itself read only:
Log Files usually at: C:\Documents and Settings\All Users.WINDOWS\Application Data\Comodo\Personal Firewall\Logs
Right click the file and make it read only. This drastically reduces the drain on your system in most cases. Worked for me and many others.
