Since it's a paid program, the obvious answer is to ditch it and use freeware. Are you willing to do that?
I don't see how this is an "obvious answer". I am no fan of Norton and love that there are freeware alternatives available, but if I pay for something I would rather get my money's worth from it. If it could be configured to run in a way that I could live with, which is what I think tg1911 is getting at.
IOW, if you installed the firewall part of Norton Internet Security (NIS), while Kerio is still installed, I would try uninstalling Kerio or the Norton firewall and make sure you have nothing else running that would conflict. According to PCMag, the 2007 version of NIS reduced the amount of resources required. If you can get it to run this way I would keep it at least til the subscription expires, then maybe try something else.
If you go with uninstalling the Norton firewall and keep Kerio, you should also look into whether Norton AV's Internet Worm Protection is enabled. I think it is supposed to be a HIPS feature, but it behaves like a firewall and some people I've dealt with have solved some problems with internet access by disabling it.
There are certain advantages to having a commercial AV installed. Scheduling of updates and full system scans along with Norton's generally good detection rate would be the most important. Also better product support, but with Norton as an exception there as you've pointed out. Used to be their email support was pretty good but they charge for phone support. There are other AV's better at this.
If you are pretty experienced in security matters, then personal support is not that big of a factor. You won't get any one on one personal support from the free AV's, altho most now have forums where you can get help from your peers and of course, this forum.
As I said, I'm all for freeware alternatives. I recommend them to people all the time especially when I see they have an older verison of Norton that's dragging down their system. McAfee and Trend Micro as well lately. But the two mentioned here do not have a great detection rate. People who use them and recommend them usually have enough knowledge to protect themselves and prevent getting infected in the first place. But if you do any high risk surfing and tend toward unsafe practices such as opening email attachments and instant messaging links without checking them out first, then I would stick with a commercial AV--especially if I had already paid for it.
If you do go for a switch to freeware, however, I've been hearing a lot of good reports about Avira's Antivir
freeware AV. It's been known to detect some of the newer malware even before some of the commercial ones. I'm not sure if it's user interface is very user friendly tho--been meaning to give it a try but haven't had much time lately.