There are several other threads on iSight, and how it interfers with Capture from other devices. Some of the Mac-folk has solutions, or workarounds, but I do not recall the exact steps.
Does not address the lack of the HD Presets though. Unless others have direct solutions, you might want to try a Repair Installation from the DVD's. If these Presets were not initially installed, a Repair Install might install them.
If you are using a trial version of Premiere, then this comes with no facilities for capture and editing of HDV.
If you are using a full, activated version, then have you updated it to v4.1? If so then this could be the problem; there have been reports of the update process apparently changing the installation back to a trial version in that the HDV preset disappear.
Let me guess, you updated to 4.1, you have the full paid version, you may have tried in the past the trial version and now, after updating it no longer works. Is this correct?
If so, there is one cumbersome and time consuming solution, uninstall, run Cleanscript 2 or 3 times, reboot after each Cleanscript run, and then reinstall.
If my guess is not correct, contact TS.
what is Cleanscript