Your home router likely has the ability to forward ports, so the ddwrt router should not be necessary, just a nice to have.
First step would be to sign up for some dynamic dns service. They will map a domain name to whatever your current public facing IP address is. These are are often subdomains like
angelassh.somedyndns.org... log into your router first and look around, it's possible it may already support one.
If not, you can still update the service from any of your home computers using downloadable clients or scripts like wget or perl. The update process will be explained by the dynamic dns service.
Once updated, your friends should be able to reach your dynamically assigned ip address using the example
angelassh.somedyndns.org domain. This domain should point to whatever http://www.whatismyip.com says your public facing ip address is.
By the way, you can also just send your friends that public facing IP address and skip the dynamic dns stuff if you want. Just remember that it can change so your friends would have to update their settings.
Either way, you will need to forward the SSH port to your computer's private ip address, and of course make sure you have an ssh server running on your local computer.
It's also possible that your ISP may block port 22, so keep that in mind. If so, you could (and really should anyway) forward a higher port number instead.. ie: Forward port 2222 in your router to your private ip address. This will help keep the autobots from trying to guess your ssh login.
When it is all said and done you should be able to
ssh -P 2222 email@example.com or just
ssh firstname.lastname@example.org if you go with the default ssh port.
Also, your home computer will now be subjected to the interwebs and all of its cooties.. Keep your system patched, updated and firewalls on.
Hope this helps!