I use
Finale personally. It works great for beginners, intermediates, and masters alike. You can play into it using an electronic piano or you do it note by note. It's one of the best programs to arrange pieces in the world =). I wouldn't use it for sounds though ;P.
As for singing, let's see... I honestly don't know what to say. I've been able to sing all my life, so... I guess it's just because I sing every day for a few hours... I sing to work, sing home, sing during breaks, sing at night, sing here, there, and everywhere. Maybe just sing a lot? that'll help ; ). To get your voice tuned, playing a musical instrument helps a lot. You don't have to sing to it, just play it. Singing to it helps as well though, um.
Kudos to you ^_^