+1 on the AVG! just for spam and crap Lavasoft works great!Looks like a great build. I would suggest kicking up the ram another 1Gig however.
AVG offers a decent set of options for that software.http://grisfoft.com or just google FREE AVG/ I would stay away from the norton suite as the overhead is awful. At the very least you can run the AVG antivirus (free version is fine for home)
Windows defender is also pretty nice (Used to be Giants program)
For home setups I always suggest that you get a router. This provides something of a poor mans hardware firewall. Hackers cant hack what they cant see. This puts your computer behind something of a safety wall.
Windows firewall is just fine by itself. Do not try and run 2 or more firewall programs as they play poorly together.
Lavasoft free