The only thing you have to do to access your raspberry from internet is the following:
Some details of my configuration (file '/etc/ddclient.conf'):
daemon=60 syslog=yes mail-failure=PUT-HERE-AN-EMAIL-ADDRESS-WHERE-ALL-FAILURES-WILL-BE-SENT ssl=yes protocol=dyndns2 use=web, web=myip.dnsdynamic.com server=www.dnsdynamic.org login=PUT-HERE-YOUR-USERNAME-OF-DNSDYNAMIC.ORG password='PUT-HERE-YOUR-PASSWORD' PUT-HERE-YOUR-DYNAMIC-WEB-ADDRESS.com
And finally:
# update-rc.d ddclient enable
To add it in the default runlevel.