Is it ok to have more than one firewall?

No, I don’t believe AVG 8.0 free has a firewall.

As to how many you need, it’s best summed up with a line from a
movie:

“There can be only one.”

Why, and which one, deserves a little explanation.

Software firewalls have to work at a very low level in order to
protect your system. By “low level” I mean that when something comes
across your network connection you want the firewall to be one of the
very first pieces of software examining the data.

While conceptually it’s possible to have more than one piece of
software doing that job, the reality is most software firewalls are
simply not designed to play well with others. When enabled, they assume
that they are the only firewall. The net result is that they can
interfere with each other.

To be honest, I wish that they would check, and at least warn if
they find another firewall is in operation.

As an aside: note that I’ve been careful to refer to them as
“software firewalls”. It’s certainly possible, safe and in some cases
even desirable to have a hardware firewall, such as a router, in
addition to a single software firewall.

So in your case, which one do you want?

I’m not at all familiar with Earthlink’s firewall. However, I’m going
to assume it’s one of the popular commercial ones like ZoneAlarm or
Comodo that came bundled with your system.

The Windows built-in firewall is a good solution for many
situations. As I’ve mentioned before I’m behind a router as my firewall
at home, but do enable the Windows firewall when I travel. It’s easy,
no extra installation or management is required, and it’s always
there.

That being said, most of the other software firewalls “do more”;
particularly when it comes to outbound threat detection. Like a
hardware firewall, the Windows firewall is focused mostly
(though not exclusively) on protecting you from external threats. Other
software firewalls will also monitor outgoing network traffic to see if
there is something suspicious going on within your machine. They’ll
frequently block external access attempts that aren’t known to be safe,
for example.

None of that answers the question: which one do you want?

I’m going to say it’s personal preference.

If you want the comfort of a little more protection, then perhaps
enabling the Earthlink firewall is the way to go. Personally, I’m not a
big fan of outbound protection, because by definition it’s too late –
if outbound protection catches something real, then it’s because you’re
infected with malware or have some other problem. My preference is to
focus on inbound protection and other good behavior to prevent ever
needing outbound protection.

The Windows firewall is certainly good enough for most usage.

And finally, if you’re already behind a router, you may not need
either. That’s how I run here at home. A hardware based firewall gives
me all the inbound protection I’m looking for.

The bottom line: you’ll probably be fine with either, but not
both.