sequencing music with Vista OS...tech support needed

I bought a new lap-top and had visions of sequencing (is that what it's called) some music as a hobby. I've got a Yamaha portable keyboard and once did some sequencing with my old Amiga using a program called Dr. T. My problem is I can't seem to find sequencing software that will operate with the Vista OS. I am guessing the software will catch up with this system but does anyone know of, or recommend, software that works now?