I got an answer from a PM I sent one of the Admins there, and this is what he wrote:
"Let me try to remember now, it's been ahwhile since I added that option.
You can start by adding a User Profile Field, via the "User Profile Field Manager" in your vB acp.
Example: xFire. Single-Line. Text Box.
You will then need to add some code in your templates. Let me look around and see if I can find what template and the code and I will get back to you."
Always a start
