There were several people interested in the previous topic so let me add some supplement. The idea of this blog is to publish "shorts" you can see it and grab it fast, so (of course) this is absolutely not the full story, not at all (of course).
As I said before using only placeholders is not a good idea, but there is a solution you can use if you really don't want to use labels. It is a dynamic placeholder that does not disappear when a user starts to type but moves to the top of the field (1).
This is a good solution but not for extended form with many fields.
And second - this is always a good idea to give a hand to users, give them some tips like small "information" icon next to the field. You can just use rollover (hover) tooltip when help text is really short or link it to pop up (but better not) or subpage.
And this is an old controversy - you should use "_blank" window in your link href or now. In my opinion - yes.