Hey VI... As Far as I can see AVG v8 doesn't have a Firewall.
AVG Antivirus 8 Internet security and firewall reviews - CNET Reviews.
You might try Port Forwarding your Linksys Router as they are renowned for problems.
Port Forwarding for the Linksys WRT54G.
Since AVG has no Firewall, you might check your Windows Firewall to make sure LW has Full Access.
After further review, You might Reconsider Using AVG v8. See Below Link
Say it ain’t so AVG, say it ain’t so: AVG LinkScanner = Badware? | Zero Day | ZDNet.com