Firewall: Hardware.
Antivirus: F-Prot Antivirus, small and secure. 👍 The residential scanner (the thing that scans everything in the background 24/7) is only using just over 1mb of ram, and with the Scheduler enabled (automatic updates and such) it's only using about 3mb in total. Not to mention it has about a 98% detection rate and some pretty decent scan rates (faster then Norton by far). I don't know why all these people go for Norton... it's the biggest resource hog ever with the slowest scan rates I've ever seen.