Simple Q&A wordpress plugin and pop-up login

Hi there,

My client would like to add a Q&A section to his website much like the one used here on this website (The Ask Alex section): http://www.thenakedceo.com/ask-alex. It will have a secure login for those wanting to ask questions but the answers will be public.

Could anyone recommend a plugin that can give me the same simple Q&A functionality as stipulated on that website or is it something that I need to get a web developer to do?

Also, my client would like a pop-up window on the homepage that allows people to register or login from the homepage. What is the best plugin to use for this?

Thank you so much for your help.

Cheers,
Lydia