In order to add a shell account to my authenticated github acc list, I need to retrieve it's public SSH key; how can I do that either in putty, or via bash directly?
You need to create a key. This key will be unique to your account. I'd suggest you take a look at: http://pkeck.myweb.uga.edu/ssh/
Here is an excerpt from that site:
The id_dsa.pub file is what you are after.