Whatever you do, make sure if you are going to use the free Kerio firewall from Sunbelt that it is version 744 because the previous versions caused many users - certainly not all - BSoDs.
I speak from painful personal experience. It was here for the first time that someone read my Minidumps and it always pointed to the same driver -- in three different versions of Kerio.
However, since installing version 744, their latest, I have not experienced [knock on wood, salt over the shoulder, fingers crossed] any crashes. They fixed a lot of issues. See below:
This is taken from the "readme". Looks like Sunbelt has woken up in 2007!
* Corrected issue in which registration fails when firewall is enabled.
* Significant improvement in network performance when web filtering is enabled.
* Enhanced Process Injection prevention to prevent code inject attempts into Windows system DLLs.
* Corrected numerous application crashes in the firewall service.
* Corrected various crashes in assist.exe
* Corrected issue in which setting password and checking for update does not cancel authentication form.
* Corrected issue in which binary data appeared in logs.
* Significant improvement in product stability.
Now this may sound strange, but otherwise I like this Firewall. It passes Shields UP! 100% (realizing that this is only one test) and it is very flexible for personal configuration.