you are correct, you do not have an on setting for your flash (what the heck is fill-in mode?) you have kick ass telephoto zoom though, 10X is awesome. So long as you are goofing around why not try the 50 speed as well, and mess with the shutter speed too, maybe 1/60 and 1/40 with a steady hand or a tripod (although the fact that you have only a 10 second delay may be a problem for tripod use). That noise is definitely sensor noise not dirty glass, but cleaning the glass really well is always a good idea before taking pictures.
edit 1: http://www.dpreview.com/reviews/specs/Konica_Minolta/minolta_dimagez1.asp
Edit 2: Use fill in mode, it is a flash to light the foreground, slow sync goes off slightly before the picture is taken and for slightly longer to fill in the background.
edit 1: http://www.dpreview.com/reviews/specs/Konica_Minolta/minolta_dimagez1.asp
Edit 2: Use fill in mode, it is a flash to light the foreground, slow sync goes off slightly before the picture is taken and for slightly longer to fill in the background.