Which web technology to learn for an experienced C++ developer?
Before learning either of these, spend some real time and learn HTML and CSS in depth.  Also learn Javascript and JQuery (or your favorite client side library).  The O'Reilly books on the topic are pretty much all good IMO.
I say that because I think that you'll find that for most modern web sites, a lot of richness is moving to the client side, and away from the server side.  Under this model, your code in PHP or JSP is probably going to look pretty similar (ie, fetch data from the database and serve it to your view or into JSON for the client to consume).
Friends, 
I've got some exp in c++ and now kind of starting my way to J2EE (to survive:))). Meanwhile, I've got a plan to venture in to a web portal my own. But with very little experience in web technology, I'd need to start from scratch. I'm little confused on which way to go and I'm here. 
PHP, Python or JSP, considering the fact that, anyway I've got to learn J2EE at my work.
Would that be worth to learn PHP or Python to develop a portal which I expect to get 80-100K 
hits per day "IF" everything goes well OR jsp would be sufficient? 
Many thanks