Debian send ip address on startup (sheevaplug)

I'm having a sheevaplug with debian (default) installed on it.

I would like to receive a mail with the ip-address of the sheevaplug, everytime it is restarted, AND everytime the ip address changes.

I have no idea how to do this...

I realize I'm asking multiple things at once, so part of the solution is also ok:

how to write something that runs on startup?
how to send a mail?
how to detect a change in ip address?
how to retrieve the correct ip address? (ifconfig gives a lot of information I don't need)

Thanks!

Solution

If dyndns (see @taspeotis' answer) is not what you want, you can:

run commands once a network interface comes up by using the post-up hook of ifup (see man interfaces(8)
send email: echo "mail body" | mail -s subject recipient@foo.bar
detect changes of ip-address: this will probably happen if you use dhcp, if you're using dhclient you could use its /etc/dhcp3/dhclient-enter-hooks.d
get the correct ip address: ifconfig eth0 | grep "inet addr"