At present, most computers and certainly the Vegas software is not up to editing HDV nativly in an easy and satisfying way, so you must use an intermediary format somehow.
The lasted ConnectHD works very well. It has scene detection and an excellent quality codex. I do only HDV and that's what I use, but you will still need a moderately fast, middle of the road machine. If you have a low-end machine look at a very good, and much cheaper alternative to ConnectHD called "GearShift". Gearshift is a script that uses the internal Vegas intermedairy file conversion to make avi's for editing, but it is not a capture utility like ConnectHD which can also capture and convert to 24P on the fly that it does very well.