Norton personal firewall 2003

Hi everyone, I had a quick question. I am going to be networking two pc’s for a small business I run. I have installed Nortons latest firewall. After surfing online a bit, I notice that the surfing is slowed down some with the firewall enabled. Is this normal for a firewall? Of course the salesman said the surfing will be faster due to ad blocking features etc. I would think it would be a bit slower because everything is filtered through the firewall, but I could be wrong. I am using Windows XPpro and a 56k dial up connection. Thanks alot!!