I recommend both AVG for anti-virus software and Kerio Personal Firewall and ZoneAlarm for firewall software. All come in free versions for home use, and all good products as well.
AVG runs a continous on-access scanner so that whenever a file is opened, downloaded or copied it is checked for viruses. Or you can run an on-demand scan to check for viruses whenever you want. You can also schedule a complete system scan to be run once a day. Finally, you can schedule it automatically check for new virus database updates once a day as well. I don't know how it compares with PC-Cillin since I've never tried that product. Of course, if it is already loaded on the computer and working, that gives it one leg up!
I think the biggest downside to AVG is that the database updates are not incremental. Each time it needs an update, it has to download the whole ~1.5 MByte file. This is no problem if you have a high-speed Internet connection, but if you have a slow 56K modem the incremental updates of Norton and McAfee are a nicer.
Kerio Personal Firewall is an excellent product. It is very configurable so in the right hands it can really be great. However, all that configuration can make it kind of bewildering to an inexperienced user. Because of that, I generally recommend Kerio for experienced users and ZoneAlarm for inexperienced users.
If I recall the license agreements I clicked through when installing these products (I actually do skim through them), although all of these have free versions for home use, none are free for business use, even if it is just a small business.
Whatever software you choose, be sure to test your installation. Here are some resources.
(Look for "Shields Up!". It should be here