Symmetric NAT: What is it, and what can I do about it?

Hi,

I'm pretty frustrated... A while ago I installed IPv6. It didn't work
and after some investigation I found the reason to be my Netgear WGR614
v3 (wireless router) being a Symmetric NAT. IPv6 apperantly doesn't
support Symmetric NATs.

What is a Symmetric NAT? If I understand correctly, the difference
between this and other types of NATs is that it only lets traffic
through if the same ports are used on both the remote and the local
hosts. What's the point? Why would they do that?

Now, my most important question: Can I do anything about it, other than
get a new router?

On a different note: My eMule is causing me trouble, could it be
related? (It's slow, and it completely jams my connection, making any
other activity on the net impossible - even when I limit it to
ridiculously slow upload speeds)

Thanks in advance for any input,

Noam Nelke, Israel.