Worried about having been hacked

[James Allsopp]

Hi,
I've a Fedora core 10 system which spends a lot of the time connected
directly to the internet, with a static ip. The only external ports open
are 80 and 22. SSH only allows access to one non-root user via an rsa
key. I'm using an IPtables script from

> http://iptables-tutorial.frozentux.net/iptables-tutorial.html

However, I normally get my logs e-mailed to an external account and
they're not getting to me. I'm not sure if they've not been sent or my
logs are being altered and hidden. How do I diagnose this problem, and
in general look for security incursions. I'm thinking of leaving
wireshark running on the external ethernet card and see what happens.

Thanks, any advice much appreciated.
Jim