Is there a way to automatically sync iTunes to my music folder (which is on a different hd)?
No, iTunes will not "listen" for music in a given folder (like the popular BT program Transmission, which will load torrent files once they've been downloaded to a given directory).

You have to manually add music by dragging it in the iTunes window or going through the file menu (CMD + O).

However, you could achieve what you are after perhaps with some voodoo in Apple Script. Or simply sort the contents of your music folder by "date added" (provided you are using Lion) and manually add the songs as they arrive.

But then if you are going through all this trouble of manually managing files, you may wish to ask yourself, "why"? It might be less of a burden to just let iTunes do its thing (like it was mentioned before, you can tell iTunes to copy the music anywhere you like, on any drive connected to your system, even on a network) than micro-manage a bunch of files.