1. If you are using a postbit like it is set out here at vB.org, then you are using the postbit_legacy (user info is on the SIDE) if your user info is at the top, above the post words, you are using the postbit.
2. Templates are, simply, the code behind the display of your vBulletin pages and such.
3. Make sure you check the WHOLE template since a piece of code can occur more than once. But, a previous hack you may have installed could have edited the way that specific line has been placed in your template. If there is no other instance in the template, I'd place it after the last part of the code that you were looking for. (That is assuming it says "after it, place")
4. Can't help you there, sorry.